Introduction
Daucus carota
L. var. sativa DC is a variant of wild carrot (D. carota L.
var. carota), belonging to Apiaceae. It has a long history of cultivation, with
extensive planting areas worldwide. Carrot seeds are small with leathery skin
containing volatile oil, resulting in poor water permeability (Zhuang et al. 2006). Carrot is rich in vitamin A and β
carotene, which could effectively prevent night blindness, delay aging, and
strengthen immunity (Imsic et al. 2010). Seed soaking with exogenous
hormones (such as GA3 and IAA) is a common approach in production of
crops, such as tomato (Luo et
al. 2015), tall
fescue (Xu et al. 2008), lettuce (Zagorski and Lcwak 1983) and
radish (Jabir et al. 2017). Soaking
seeds with exogenous hormones has a significant effect on the development of
organs, such as the roots, stems, and leaves of the plant seedlings (Pill and Finch-Savage 2008).
Exogenous hormones at certain concentrations can promote the growth of plant
stems (Barratt and Davies 1997), affecting the performance of crops, such as cucumber
(Qian et al. 2018), corn (de Souza and MacAdam 2001) and pea (Ross et al. 2000). Exogenous hormone
could promote the growth of plant stems by increasing the number and length of
cells or by altering the extensibility of the cell wall (Wolbang
et
al. 2004). For
example, induced by exogenous GA3, cell cycle progression in rice
stems could be shortened and the number of cell divisions could be increased,
thereby affecting the morphology of rice (Wang
et al. 2013). Furthermore, exogenous GA3
not only promotes the growth of stalks by promoting the division of pea cells,
but also affects the endogenous IAA content in metaphase cells of pea seedlings
(Barratt and Davies 1997). However, the rapid growth
rate of plant seedling stems could cause vein growth and lodging, which is not
conducive to the growth and cultivation of seedlings. Therefore, it is
important to study the mechanisms by which exogenous hormones promote stem
growth.
In carrot production, seed soaking
in exogenous GA3 or IAA is a common method (Lee 1990). Hormone treatment not only
promotes the germination of carrot seeds, but also changes the morphology of
plants by promoting the growth of seedlings (Barratt and Davies 1997). Changes
in plant morphology are mainly due to changes in the cellular structure, which
are determined, to some degree, by endogenous hormones in the plant (Li et al.
2019). Therefore, with the treatment of carrots with exogenous hormones, the
relationship between exogenous hormones and the content of endogenous hormones,
cell structure and morphology of carrot seedlings was explored. The effects of
soaking with exogenous hormones on the growth and development of stems in
carrot seedlings were further explored. The mechanism of action of hormones on
carrot seedlings is to select the most suitable exogenous hormone treatment for
carrot soaking, which provides a certain theoretical basis for obtaining
high-yield and high-quality carrot seedlings in production. It is of great
significance to improve the growth and development of carrot seedlings in
production. Variation in the external morphology of plants is closely related
to variation in physiological indexes. Morphological differences can better
reflect the internal physiological and cellular changes of carrots (Pill and Finch-Savage 1988). Three
concentrations of GA3 and IAA were evaluated in this experiment.
Accordingly, the GA3 and IAA treatments with the largest
morphological differences were first screened, and then the endogenous hormone
contents were measured and cytological observations were performed to better
reflect the physiology and cellular characteristics.
Materials and Methods
Materials and treatments
As test materials, Yibo Dadi carrot (D.
carota L. var. sativa DC) seeds were obtained from Tongdeli
Seed Industry Co., Ltd., Qingdao, China. This study was performed at the
Vegetable Research Institute of Fujian Agriculture and Forestry University from
January 1–23, 2019. Test seeds were divided into the
following treatment groups: distilled water (CK), three gibberellic acid (GA3; 50, 150 and 250 mg·L-1) and three indole acetic
acid (IAA; 50, 150 and 250 mg·L-1). After soaking seeds for 12
h, they were germinated at 30°C for 24 h and sown in the seedling substrate.
Each treatment was repeated 3 times, and 100 carrot seeds were used for each
repetition. The first day was seeded on the nursery substrate, and the test
period was 20 days.
Morphological indices of the
carrot stem
The test period was 20 days. Three seedlings with the
same growth potential were selected for each treatment to determine the plant
attributes. The plants were cleaned, and the stem diameter, stem height, and
plant height were measured using a Vernier caliper. In addition, 30 strains
were randomly selected from each treatment, and the plants were cleaned. The
fresh weights of the aboveground and underground parts were measured, and the
plants were placed in an oven (Model: DHG-9141A; Shanghai Jinghong
Experimental Equipment Co., Ltd., Shanghai, China) and dried at 90°C for 1.5 h.
Then, the dry weights of the aboveground and underground parts were determined.
The aspect ratio of the stem is
defined as the ratio of the stem length to stem diameter; it reflects the
growth of plant shoots. The ratio of the root to shoot is the ratio of the dry
weight of the lower part to the dry weight of the shoot, reflecting the growth
of the whole plant (Chinchilla‐Ramírez et al. 2017). The stem aspect ratio was
estimated according to the following formula:
Stem aspect ratio (%) = (Stem length/stem diameter) × 100
Where the stem diameter is measured
at 1/2 the length of the stem
Determination of endogenous hormone
contents in carrot seedling stems
Enzyme-linked immunosorbent assays were used to determine
endogenous hormone contents in carrot straw (O'Kennedy et
al. 1990). A 0.2 g
carrot stem segment was fully ground with liquid nitrogen, supplemented with 2
mL of extraction solution (containing 1 mmol/L BHT (Di-tert-butyl p-cresol) and
80% methanol mixture), ground in an ice bath, and maintained at 4°C for 4 h.
After centrifugation at 1150 g for 8 min, the supernatant was obtained and 1 mL
of extraction solution was added. The above steps were repeated twice, and the
supernatants were combined. The supernatant was treated with a C18 solid-phase
extraction column (Beijing Dikema Technology Co.,
Ltd., Beijing, China), and the samples were transferred to a 10 mL centrifuge
tube. The methanol in the extraction solution was removed using a Cetivap 78120-03 centrifugal concentration dryer (Labconco, Kansas City, MO, USA). The volume was fixed to
0.4 mL of the sample diluent (including 1% Tween-20 and 1 g/L gelatin in PBS
with pH 7.5). An IL-10 ELISA Kit (Thermo Fisher
Scientific) and enzyme-linked immunosorbent spectrophotometer were used to
measure the concentrations of the standards and the OD values at 490 nm for
each sample. The concentrations of different endogenous hormones in each
treatment were calculated by drawing the standard curve.
Microscopic observations of whole plants
and stem sections
On day 20 of the experiment, images of whole carrot
seedlings were obtained using a 20-megapixel digital camera (Nikon, Tokyo,
Japan; COOLPIX S2800). For microscopic observations of longitudinal sections of
carrot stems, on day 20 of the experiment, 3 carrot seedlings with uniform
growth were randomly selected from each treatment, and 0.5 cm samples were
obtained at 1/2 the length of the stem. Then, 5 g of agar was dissolved in 100
mL of water. After melting at a high temperature in a microwave oven (Shanghai
Matsushita Microwave Co., Ltd.; NN-DS1100), the sample was poured into a
culture dish with a diameter of 35 mm, tiled, fixed in 5% agar, and cooled to
room temperature. The fixed stems were sectioned longitudinally by the
freehand-sectioning method, stained with 0.04 mg of LPI (Hai De Biotechnology
Co., Ltd., Beijing, China) dye for 10 min, washed with water to remove excess
dye and dried. The longitudinal cell structure of the carrot stem was observed
using a confocal microscope (FV1200, Olympus, Japan) at a wavelength of 535 nm.
For microscopic observations
of transverse sections of carrot seedlings stems. On the last day of the
experiment, 3 strains were randomly selected from each treatment. The same stem
segments were cut, fixed with 5% agarose, and then sectioned using an
oscillating slicer (Leica; VGA3000S) longitudinally and horizontally. The
transverse sections were observed using an inverted fluorescence microscope
(Leica DMI8). Then, the cross-sectional diameter of vascular bundle, stem
cross-sectional diameter and ratio between vascular tube diameter and the total
cross-sectional diameter of carrot stem cross-sections were measured.
Results
Influence hormones on morphological
indices of carrot stem segments
On day 20 of the test period, the stem length, plant
height, and stem aspect ratio of GA3-treated carrot seedlings were
30.47, 74.21 and 55.37, respectively, and were significantly greater than those
of other treatments, indicating that 250 mg·L-1 GA3 had
the greatest impact on carrot morphology (Fig. 1). The main manifestation was
an increase in the growth of stems; there were no significant differences in
stem aspect ratio between CK, 50, 150 and 50 mg·L-1 IAA treatments. Except for
50 mg·L-1 GA3, the root-to-shoot ratios of other
treatments were significantly greater than CK. The IAA treatment had the largest
root-to-crown ratio. A concentration of 150 mg·L-1 IAA had the
greatest effect on the growth of carrot seedlings. Different concentrations of
exogenous GA3 and IAA affected plant morphology. When the exogenous
GA3 concentration was 250 mg·L-1, the growth of stems was
greatest. When the concentration of IAA was 150 mg·L-1, the root-shoot
ratio of carrots was highest. Therefore, the endogenous hormone contents in
carrot stems were further evaluated in the CK, GA3, and IAA treatments. Observations at the
hormone and cellular levels explained the effects of exogenous hormones on the
growth of carrot stems.
Determination of endogenous hormone
contents in carrot seedling stems
The contents of the endogenous hormones GA3,
ABA, and IAA in the carrot seedling stems for the GA3 treatment was
significantly higher than those for the CK treatment (see Table 1), i.e.
12.15, 151.74 and 77.75 ng/g FW, respectively. The ZR content for GA3
treatment was 11.21 ng/g FW, which was second only to that of the CK treatment
and was not significantly different from that of the CK treatment, indicating
that 250 mg·L-1 GA3 applied to carrot seedling stems
mainly increased endogenous GA3, ABA and IAA. It is possible that
250 mg·L-1 exogenous GA3 promoted stem elongation at the
metabolic level by increasing the contents of endogenous GA3, ABA
and IAA.
The contents of endogenous GA3
and IAA in the carrot seedling stems of the IAA
treatment were second only to those of the GA3 treatment and were
significantly higher than those of the CK treatment. The contents of endogenous
ABA and ZR were the lowest. The contents of endogenous GA3, ABA,
IAA, and ZR were 11.60, 97.52, 68.31 and 7.41 ng/g FW, respectively, indicating
that the primary effects of 150 mg·L-1 IAA at the metabolic level in
carrot seedling stems were the increases in endogenous GA3 and IAA
and decreases in endogenous ABA and ZR.
Exogenous GA3 and
IAA can affect plant morphology by affecting the cellular structure (Barratt
and Davies 1997; Kim et al. 2006). In this experiment, 250 mg·L-1 GA3
and 150 mg·L-1 IAA significantly changed the endogenous hormone content
in the stem parts of carrot seedlings; accordingly, it could be speculated that
exogenous hormones at certain concentrations could alter the cellular structure
of the stem by changing the endogenous hormone contents of carrot seedlings,
which in turn could affect seedling morphology (Table 2).
Microscopic observations of whole plants
and stem sections of carrot seedlings
On day 20 of the experiment, the
morphology of carrot seedlings varied significantly. IAA treatment had the highest plant height, GA3
treatment was the second, and CK treatment was the smallest. The stem lengths
of these three treatments were A (17.80 mm), B (30.47 mm) and C (21.79 mm), it
suggested soaking with 250 mg·L-1 GA3 and 150 mg·L-1
IAA promotes the growth of both the carrot plant and stem. In particular, 250
mg·L-1 GA3 had the most obvious effect on the seedling
stem, and 150 mg·L-1 IAA had the most obvious effect on the whole
plant height (Table 3).
The longitudinal
cell structure of carrot seedling stems and phloem sites were observed, the
longitudinal cells of the stems were largest in 50
mg·L-1 GA3 treatment, with
significant increases in the length and width of single cells, followed by the IAA treatment and CK
treatment. This suggests that 250 mg·L-1 GA3 can
promote stem growth by promoting the broadening and lengthening of stem
longitudinal cells, and 150 mg·L-1
IAA could also promote the broadening and growth of stem longitudinal cells but
the effect was weaker than that of 250 mg·L-1
GA3.
Table 1: Endogenous
hormone contents in the aboveground part of carrots under different
seed-soaking treatments
|
Treatment |
GA3 content (ng/g FW) |
ABA content (ng/g FW) |
IAA content (ng/g FW) |
ZR content (ng/g FW) |
|
CK |
9.43±1.20 c |
102.39±4b |
48.36±3.82 c |
11.53±1.31 a |
|
250
mg·L-1 GA3 |
12.15±0.15 a |
151.74±5a |
77.75±2.21 a |
11.21±1.35 b |
|
150
mg·L-1 IAA |
11.60±0.24 b |
97.52±3 b |
68.31±4.10 b |
7.41±1.27 c |
Note: Data
were analyzed using the LSD multiple comparison test implemented in DPS7.5.
Different letters indicate significant differences (p < 0.05)
Table 2: Morphological
indexes of carrots under different seed soaking treatments
|
Treatment |
Stem diameter (mm) |
Stem length (mm) |
Plant height (mm) |
Root dry height (mg) |
Above ground dry weight (mg) |
Root: shoot ratio |
Aspect ratio |
|
CK |
0.53±0.03c |
17.80±0.90e |
61.70±1.47d |
1.02±0.08d |
5.35±0.31b |
0.19±0.005e |
33.79±0.21c |
|
50
mg·L-1 GA3 |
0.53±0.01c |
23.48±1.22bc |
65.32±1.31c |
1.23±0.02b |
6.14±0.38a |
0.20±0.010de |
44.35±3.12b |
|
150
mg·L-1 GA3 |
0.52±0.02c |
25.29±1.31b |
70.19±1.23b |
1.25±0.03ab |
5.97±0.65a |
0.21±0.018cd |
48.40±3.80b |
|
250
mg·L-1 GA3 |
0.55±0.03c |
30.47±2.14a |
74.21±1.15a |
1.32±0.05a |
6.02±0.29a |
0.22±0.007c |
55.37±0.87a |
|
50
mg·L-1 IAA |
0.62±0.01ab |
20.78±1.49d |
62.27±0.75d |
1.05±0.05cd |
4.19±0.24c |
0.25±0.004b |
33.50±1.89c |
|
150
mg·L-1 IAA |
0.64±0.02a |
21.79±1.50cd |
62.46±1.05d |
1.11±0.01c |
3.96±0.06c |
0.28±0.005a |
34.12±3.42c |
|
250
mg·L-1 IAA |
0.60±0.02b |
20.17±1.76de |
61.99±0.90d |
1.04±0.08cd |
4.33±0.28c |
0.24±0.008b |
33.87±3.84c |
Note: Data
were analyzed using the LSD multiple comparison test using DPS7.5. Different
letters indicate significant differences (p < 0.05)
Table 3: Cross-sectional
indicators of carrot stem segments after different soaking treatments
|
Treatment |
Cross-sectional diameter of
vascular bundle (μm) |
Stem cross-sectional diameter (μm) |
Ratio between vascular tube
diameter and the total cross-sectional diameter |
|
CK |
200.0±10b |
590.0±10 b |
0.340±0.011 b |
|
250
mg·L-1 GA3 |
180.0±5 c |
500.5±10c |
0.36±0.003 a |
|
150
mg·L-1 IAA |
235.0±10 a |
640.0±15a |
0.36±0.004 a |
Note: Data
were analyzed using the LSD multiple comparison test implemented in DPS7.5.
Different letters indicate significant differences (p < 0.05)
%20371-376_files/image002.png)
Fig.
1: Carrot seedlings on day 20 of hormone treatment
Note: A, B, and C indicate the stem length of CK,
GA3, and IAA, respectively
%20371-376_files/image004.png)
Fig. 2: Morphological observations of cross-cut fragments of carrot stems treated
with different hormones
Note: In panel a, from left
to right, the transected cell structure of the stems of carrots treated with
CK, GA3, and IAA are shown. In panel b, from left to right, the longitudinal cell structure of the
stems of carrots treated with CK, GA3, and IAA are shown
GA3 and IAA at certain
concentrations can promote the growth and differentiation of vascular bundles
in stems of plants (Fukaki et al. 2002; Xu
et al. 2008). Fig. 2 depicts the cross-sectional diameters
of the stem segments of carrot seedlings. The vascular
bundle cross-sectional diameter, stem cross-sectional diameter, and vascular
bundle diameter of the GA3 treatment accounted for the largest
proportion of the total cross-sectional diameter (235 and 640 μm, and 0.36, respectively) and the stem
cross-sectional diameter of the IAA
treatment was significantly larger than those of the CK and GA3
treatments, indicating that 150 mg·L-1 IAA has the most significant
effect on stem thickening and vascular bundle enlargement. The vascular bundle
cross-sectional diameter and the stem cross-sectional diameter of the GA3
treatment were 180 and 500 μm, respectively,
which were significantly smaller than those of the CK treatment, suggesting
that 250 mg·L-1 GA3 restricts the vascular bundle and
stem diameters, resulting in a relatively thin carrot stem. However, the ratio
between the vascular bundle diameter and the total cross-sectional diameter was
0.36, equal to that of the IAA
treatment, and the diameters for both the GA3 and IAA treatments were significantly
larger than those of the CK treatment, suggesting that 250 mg·L-1 GA3
could make the carrot seedling stem thinner. However, the ratio between
the vascular bundle diameter and total cross-sectional diameter was similar to
that of the 150 mg·L-1 IAA treatment (Table 3).
Discussion
Huang et al. (2017) showed that soaking corn seeds
with the exogenous plant growth regulator SPD can significantly increase the
endogenous SPD, gibberellin, and ethylene contents, and reduce the
concentration of ABA in embryos, thus affecting seed vigor, increasing the
germination index, vigor index, bud height, and root dry weight of corn seeds
relative to those of the control, and promoting the growth of corn seedlings
and dry matter. Furthermore, 50 μmol·L-1 IAA and 50 μmol·L-1
GA3 can promote the elongation and thickening of the stem of Narcissus
by changing the morphology of stem cells (Krug et al. 2006), indicating that the effect of exogenous hormones on
plants may be mediated by changes in the cell structure, endogenous hormone
contents, or physiological indexes. In this experiment, different
concentrations of GA3 and IAA had different effects on carrot stems.
When the GA3 concentration was 250 mg·L-1, carrot stems
were the longest among all treatments, and when the IAA concentration was 150
mg·L-1, the carrot root: shoot ratio was the largest. These results
showed that different concentrations of exogenous hormones had different
effects on carrot stems, and GA3 and IAA had the greatest effect on carrot
seedling morphology. There was a positive correlation between the differences
in plants and the differences in morphology, and the differences in external
morphology were better able to reflect the differences in the physiological indicators
of plants (Zotz
et al. 2012). Therefore, the GA3 and IAA treatments were used for further
analyses of the endogenous hormone content in carrot stems and cytological
observations to explore the relationship between exogenous and endogenous
hormone contents, cell structure, and morphological compositions of carrot
seedlings.
Certain concentration of exogenous
GA3 can induce hydrolase production in seed embryos, decompose
storage macromolecules into small molecules, promote the maturation of embryos and
the growth and development of plant seedlings, regulate plant endogenous
hormones, promote cell division and tissue differentiation, and accelerate the
growth process (Eriksson 2006). Wang et al. (2016) showed that exogenous
GA3 treatment could significantly reduce the content of endogenous
ABA in wheat seeds during germination and seedling growth, while the amylase
activity of wheat seeds was stronger and endosperm structure was fuller. In
this experiment, the contents of the endogenous hormones GA3, ABA,
and IAA in the stems of GA3-treated carrot seedlings were
significantly higher than those in the CK treatment, indicating that 250 mg·L-1
exogenous GA3 promotes stem elongation at the metabolic level via
increases in the contents of endogenous GA3, ABA, and IAA. The
contents of endogenous GA3 and IAA in the stems of IAA -treated carrot seedlings were
second only to those of the GA3 treatment and were significantly
higher than those of the CK treatment. This indicated that the effect of 150
mg·L-1 exogenous IAA on carrot seedling stems at the metabolic level
was mainly related to an increase of endogenous GA3 and IAA and
reductions of endogenous ABA and ZR. Qian
et
al. (2018)
reported that the elongation of cucumber stem segments is very sensitive
to the applied GA3, which could promote growth by changing the
content of endogenous GA3. Another study showed that IAA at a
certain concentration can promote the biosynthesis of GA1 in the
elongated internode of peas (Ross et al. 2000), thereby affecting the size of internode cells and
promoting internodal elongation. This further indicated that the application of
exogenous hormones could change the structure of cells by changing the content
of endogenous hormones, affecting plant morphology. In this experiment, GA3
and IAA significantly changed the endogenous hormone contents in seedling
stems, and can also alter the content of endogenous hormones in the stems of
carrot seedlings, which may have an effect on the cellular structure and
morphology (Table 2).
The thickening of stems and
enlargement of vascular bundles are conducive to the transport of water and
nutrients. However, the growth of stems tends to result in vein growth and
seedling lodging, which is unfavorable for the absorption of nutrients and the
growth of shoots. Therefore, it is important to study the effects of exogenous
hormones on plant stems (de Souza and MacAdam 2001; Krug et al. 2006). In this experiment, based on
whole plant analyses and longitudinal and horizontal sections of the stem, the
heights of the carrot were ranked: IAA >
GA3 > CK, and the stem lengths were ranked GA3 > IAA > CK, indicating that both 250
mg·L-1 GA3 and 150 mg·L-1 IAA can increased
the plant height and stem length of carrots, but the effect of GA3
was much stronger than that of IAA. Therefore, it is possible that GA3
may cause the growth rate of stems to be too fast during the development of
carrot seedlings, resulting in vein growth. However, chlormequat
at certain concentrations can dwarf seedlings during the seedling stage,
increasing robustness (Jiang et al. 2010). Therefore, in the actual production of carrots, seed
soaking with GA3 could result in a high germination rate, and chlormequat can be applied at the seedling stage to
alleviate the effect of GA3. The specific approach requires further
studies. GA3 could promote the growth of plants by promoting cell
division (Sauter et al. 1995; Wang et al.
2015). For example, induced by GA3, the cell cycle
in rice stems could be shortened and the number of fission events could be
increased, which resulted in continuous rice stem growth (Mao et al. 2018), while exogenous IAA
affected cell elongation by adjusting the extensibility of cell walls (Barratt
and Davies 1997). In this study, stem longitudinal cells were largest with GA3
treatmen, with an obvious increase of the length and
width of single cells, following by the IAA treatment, indicating that GA3
could promote stem growth by promoting the broadening and growth of
longitudinal cells. The cross-section diameter of vascular bundle and stem
cross-sectional diameter of the GA3 treatment were the smallest, at
180 μm and 500 μm,
respectively. However, the vascular bundle diameter accounts for the same
proportion of the total cross-sectional diameter as that of the IAA treatment,
indicating that the GA3 treatment makes stems thinner. However, with
respect to the cell structure, the ratio of the vascular bundle area to the
total cross-sectional area was the same for both GA3 and IAA.
Conclusion
Except for above ground dry weight, all morphological
indicators of CK treatment in this experiment were smaller than other
treatments, indicating that exogenous GA3 and IAA soaking carrots
had certain positive effects on carrot seedlings. In particular, 250 mg·L-1
GA3 and 150 mg·L-1 IAA had the greatest effects on
the morphological properties of carrot seedlings. Our results indicated that
carrot stems are longest after treatment with 250 mg·L-1 GA3,
and the ratio of carrot roots to shoots was the largest in response to 150 mg·L-1
IAA. Therefore, exogenous hormones could change the shape of stem cells by
affecting the content of endogenous hormones in carrot seedlings, increase the
size single cells in stems, promote the growth of stems, and affect the
appearance of carrots. Accordingly, 250 mg·L-1 GA3 and
150 mg·L-1 IAA were optimal for soaking carrots. The observed
changes in hormone contents and cellular morphology during the seedling stage
provide a basis for the selection of appropriate concentrations of exogenous
hormones for large-scale carrot production.
Acknowledgements
This work was financially supported by a) Major special
subject of science and technology of Fujian Province "breeding and
industrialization of new varieties of high yield, high quality, stress
resistance and wide adaptability of protected vegetables" (No.: 2018NZ0002-2);
b) National key joint scientific research project of green stem vegetables
(No.: 111821301354052283); c) Fuzhou Science and technology project
"collection of germplasm resources of non-heading Chinese cabbage and
breeding of heat resistant varieties" (No.: 2018-G-37)
References
Barratt NM, PJ Davies (1997). Developmental changes in the gibberellin-induced growth
response in stem segments of light-grown pea genotypes. Plant Growth
Regul 21:127‒134
Chinchilla‐Ramírez M, EJ Borrego, TJ Dewitt, MV Kolomiets, JS Bernal (2017). Maize seedling morphology and defence hormone profiles, but not
herbivory tolerance, were mediated by domestication and modern breeding. Ann
Appl Biol 170:315‒332
De Souza IR, JW MacAdam (2001). Gibberellic acid and dwarfism effects on the growth dynamics of B73
maize (Zea mays L.) leaf blades: A transient increase in apoplastic
peroxidase activity precedes cessation of cell elongation. J Exp Bot 52:1673‒1682
Eriksson S (2006). GA4 is
the active gibberellin in the regulation of LEAFY transcription and Arabidopsis
floral initiation. Plant Cell Online 18:2172‒2181
Fukaki H, T Satoshi, M Haruka, T Masao (2002). Lateral root
formation is blocked by a gain-of-function mutation in the SOLITARY-ROOT/IAA14
gene of Arabidopsis. Plant J 29:153‒168
Huang Y, C Lin, F He, Z Li, Y Guan, Q Hu, J Hu (2017). Exogenous spermidine improves seed germination of sweet corn via
involvement in phytohormone interactions, H2O2 and relevant gene
expression. BMC Plant Biol 17; Article 1
Imsic M, W Sonja, T Bruce, J Rod (2010). Effect of storage and cooking on β-carotene isomers in carrots (Daucus
carota L. cv. ‘Stefano’). J Agric Food Chem 58:5109‒5113
Jabir BMO, KB Kinuthia, MA Faroug, FN Awad, EM Muleke, Z
Ahmadzai, L Liu (2017). Effects of gibberellin and gibberellin biosynthesis inhibitor
(paclobutrazol) applications on radish (Raphanus
sativus) taproot expansion and the presence of authentic hormones. Intl J Agric Biol 19:779‒786
Jiang Y, Y Peng, ZH Li, ZH Li, ZH. Wu, SQ Ren (2010). Effects of
paclobutrazol, uniconazole and chlorcholinchloride on dwarfing of Zamioculcas
zamiifolia. Acta Hortic Sin 37:823‒828
Kim SK, SY Park, SC Lee, IJ Lee
(2006). Altered fine structure of amylopectin is induced by exogenous
gibberellin during rice grain ripening. Kor J Crop Sci 51:523‒526
Krug BA, BE Whipker, I Mccall, JM Dole (2006). Narcissus response to
plant growth regulators. HortTechnology 16:129‒132
Luo FC,
YM Guo, J Peng, XH Duan, WH Xu, C He, FG Guo (2015). Effects of
exogenous hormones treatments to release seeds dormancy of Setaria
sphacelata cv. Narok. Pratacult Sci 32:406‒412
Lee HS (1990). Effects of pre-sowing seed treatment with GA3 and IAA on flowering and yield components in peanut. Kor J Crop Sci 35:1‒9
Li A, G Chen, X Yu, Z Zhu, Z Hu (2019). The tomato mads-box gene slmbp9
negatively regulates lateral root formation and apical dominance by reducing
auxin biosynthesis and transport. Plant Cell Rep 38:951‒963
Mao JP, D Zhang, X Zhang, K Li, Z Liu, Y Meng, L Chao, YH Ming (2018). Effect of exogenous indole-3-butanoic acid (IBA) application
on the morphology, hormone status, and gene expression of developing lateral
roots in, malus hupehensis. Sci Hortic 232:112‒120
O'Kennedy R, M Byrne, C O'Fagain, G Berns (1990). Experimental
section. a review of enzyme-immunoassay and a description of a competitive
enzyme-linked immunosorbent assay for the detection of immunoglobulin
concentrations. Biol Edu 18:136‒140
Pill WG, WE Finch-Savage (1988). Effect of combining priming and plant
growth regulator treatments on the synchronization of carrot seed germination. Ann Appl Biol 113:383‒389
Qian C, N Ren, J Wang, Q Xu, X Chen, X Qi (2018). Effects of exogenous
application of CPPU, NAA and GA4+7 on parthenocarpy and fruit quality in cucumber (Cucumis sativus
L.). Food Chem 243:410‒413
Ross JJ, DP O'Neill, JJ Smith, LHJ
Kerckhoffs, RC Elliott (2000). Evidence that auxin
promotes gibberellin A1 biosynthesis in pea. Plant
J 21:547‒552
Sauter M,
SL Mekhedov, H Kende
(1995). Gibberellin promotes histone h1 kinase activity and the expression of
cdc2 and cyclin genes during the induction of rapid growth in deepwater rice internodes. Plant J 7:623‒632
Wang GL, F Que, ZS Xu, F Wang, AS Xiong (2015). Exogenous gibberellin altered
morphology, anatomic and transcriptional regulatory networks of hormones in
carrot root and shoot. BMC Plant Biol 15; Article 290
Wang LL, XY Chen, Y Yang, Z Wang, F Xiong (2016). Effects of exogenous gibberellic acid and
abscisic acid on germination, amylases, and endosperm structure of germinating
wheat seeds. Seed Sci Technol 44:64‒76
Wang X, F Han, M Yang, P Yang, S Shen (2013). Exploring the response of
rice (Oryza sativa) leaf to gibberellins: A proteomic strategy. Rice
6; Article 17
Wolbang CM, PM Chandler, JJ Smith, JJ Ross (2004). Auxin from the
developing inflorescence is required for the biosynthesis of active
gibberellins in barley stems1. Plant Physiol 134:769‒776
Xu Z, QM Wang, YP Guo, DP Guo, GA Shah, HL Liu (2008).
Stem-swelling and photosynthate partitioning in stem mustard are regulated by
photoperiod and plant hormones. Environ Exp Bot 62:160‒167
Zhuang FY, ZW Zhao, XX Li, H Hu, ZY Fang (2006). A core collection of chinese traditional carrot germplasm. Acta Hortic Sin 33:46‒51
Zagorski S, S Lcwak (1983). Interactions between hydrogen cyanide,
gibberellin, abscisic acid and red light in germination of lettuce seeds. Physiol Plantarum 59:95‒98
Zotz G, P Hietz, G Schmidt (2001).
Small plants, large plants: the importance of plant size for the physiological
ecology of vascular epiphytes. J Exp Bot 52:2051–2056