Plant Growth Regulation

To better understand the role of polyamines (PAs) and their metabolism in responses to chilling stress in tobacco plants, this study investigated changes of endogenous PA contents, PA synthetase and oxidase activities, seedling growth and membrane permeability in tobacco (Nicotiana tabacum) cvs. MSk326 (MK, chilling-sensitive variety) and Honghuadajinyuan (HD, chilling-tolerant variety) under chilling stress. Chilling stress significantly reduced the shoot and root dry weights but improved PA contents, especially of putrescine, in the two tobacco cultivars, with higher contents in the tolerant variety. Moreover, stepwise regression analysis indicated that the relative growth rate of tobacco seedlings under chilling stress was positively correlated with endogenous PA contents, putrescine and spermidine, particularly. The above results suggested that the resistance of tobacco seedlings to chilling stress was promoted mainly by putrescine and spermidine. And further study specified that the higher PA contents in the chilling-tolerant tobacco variety were related to higher PA synthetase activities [arginine decarboxylase (ADC) and ornithine decarboxylase (ODC)] and lower oxidase activities (diamine oxidase and polyamine oxidase) under chilling stress. Again, the study demonstrated that PA biosynthesis in tobacco seedlings was mainly dependent on the ODC pathway under chilling stress, through ADC and ODC inhibitor application and recovery treatments. Compared with the ADC inhibitor (d-arginine), the ODC inhibitor (2-fluoromethyl ornithine) more significantly inhibited PA contents and increased membrane permeability in tobacco seedlings under chilling stress. In summary, the research findings suggested PAs play an important role in regulating the chilling tolerance of tobacco seedlings.

Treatment of bean cuttings with 4-chlororesorcinol (4-CR), known to increase the number of roots and extend their distribution, prevented the accumulation of free indol-3-yl-acetic acid (IAA) in the hypocotyls within 24 h after cutting preparation. In mung bean there was no change in the distribution (upper half vs. 1 ower half of the hypocotyl) of IAA within the hypocotyl as a result of the treatment. In bean cuttings the treatment with 4-CR prevented the accumulation of IAA in the bottom of the cutting. Oxidation of IAA as a measure of IAA oxidase activity in bean was enhanced appreciably by 4-chlororesorcinol. The level of abscisic acid in mung bean, on the other hand, remained 3–4 fold higher than in the control, yet still about 50% lower than the zero time level. In untreated mung bean cuttings the activity of peroxidase increased after cutting preparation. In contrast, the activity of peroxidase in 4-Cr-treated cuttings was consistently lower. In order to relate to the effect of exogenously applied auxin the level of peroxidase was measured also in indol-3-yl-butyric acid-treated cuttings. The overall peroxidase activity in IBA-treated cuttings was not affected. However, when assaying for the different isozymes the drop in peroxidase activity was most evident in the inducible basic isoperoxidases both in 4-CR and IBA treatments. It appears that the exposure to 4-CR exerts an effect that is similar to that of exogenously applied auxin, affecting the activity of basic peroxidases and enhancing the oxidation of endogenous IAA, thus allowing the organization of the primordia.

The growth inhibitory effect of cucumber (Cucumis sativus L.) plants after crop harvested was investigated. Aqueous methanol extracts of the cucumber plants inhibited the growth of roots and shoots of cress (Lepidium sativum L.), lettuce (Lactuca sativa L.), alfalfa (Medicago sativa L.), ryegrass (Lolium multiflorum L.), timothy (Pheleum pratense L.), crabgrass (Digitaria sanguinalis L.), Echinochloa crus-galli (L.) Beauv and Echinochloa colonum (L.) Link, and increasing the extract concentration increased the inhibition. These results suggest that cucumber plants may possess allelopathic activity. The aqueous methanol extract of cucumber plants was divided into ethyl acetate and aqueous fractions, and the growth inhibitory activity of ethyl acetate fraction was greater than that of aqueous fraction. Thus, ethyl acetate fraction was further purified and a main allopathically active substance in the fraction was isolated and determined as (S)-2-benzoyloxy-3-phenyl-1-propanol by spectral data. This substance inhibited root and shoot growth of cress seedlings at concentrations greater than 10 μM, and the concentration required for 50% inhibition of root and shoot growth was 21 and 23 μM, respectively. These results suggest that (S)-2-benzoyloxy-3-phenyl-1-propanol may contribute to the growth inhibitory effect of cucumber plants and may play an important role in cucumber allelopathy. Thus, cucumber plants may be potentially useful for weed management in a field setting.

Phytohormones are essential for controlling abilities of plant species to overcome stress conditions, and influence some aspects of stomatal control, preventing excessive water loss. This study investigates the correlation between foliar phytohormones levels, water status and stomatal conductance in an evergreen woody species (Cynophalla flexuosa) throughout dry and rainy seasons, and the transition between them. We measured stomatal conductance (gs), xylem branch water potential (Ѱx), and leaf concentration of abscisic acid (ABA), jasmonic acid (JA), salicylic acid (SA) and trans-zeatin (tZ). Stomatal conductance was more sensitive to atmospheric conditions, such as VPD than to soil water balance. However, we found correlation between gs and Ѱx, suggesting that these direct water availability measures were a good proxy to explain gs in C. flexuosa. Moreover, ABA leaf concentration had no effect on gs, but ABA and tZ interaction was important to the phenological behaviour of this species. Cytokinins act in delaying leaf senescence, which is crucial to evergreen species, and it is opposite to ABA’s action. JA also showed a significant interaction to ABA, and kept high foliar level during wet season. ABA levels varied throughout the year, and its concentration itself was less important to gs than the interaction to other phytohormones, such as tZ and JA. In conclusion, although ABA did not directly affect stomatal conductance in C. flexuosa, the interaction between ABA, tZ and JA likely played a role in the regulation of stomatal behavior in this species.

Effects of exogenous nickel (Ni: 10 and 200 µM) on growth, mitotic activity, Ni accumulation, H2O2 content and lipid peroxidation as well as the activities of various antioxidative enzymes, such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione peroxidase (GSH-Px) were investigated in wheat roots. A considerable Ni accumulation in the roots occurred at both the concentrations. Although Ni at 10 µM did not have any significant effect on root growth, it strongly inhibited the root growth at 200 µM. Mitotic activity in the root tips was not significantly affected by exposure of the seedlings to 10 µM Ni; however, it was almost completely inhibited at 200 µM treatment. Ni stress did not result in any significant changes in CAT and APX activities as well as lipid peroxidation. However, H2O2 concentration increased up to 82% over the control in the roots of seedlings exposed to 200 µM Ni. There was a significant decline in both SOD (50%) and GSH-Px (20–30%) activities in the roots when the seedlings were treated with 200 µM Ni. The results indicated that a strong inhibition of wheat root growth caused by Ni stress was not due to enhanced lipid peroxidation, but might be related to the accumulation of H2O2 in root tissue.

Through intricate interactions with phytohormones, sodium nitroprusside (SNP), a nitric oxide (NO) donor, has a variety of impacts on plant physiology. This comprehensive review sheds light on the significance of SNP’s in plant biology under normal and stress conditions. SNP’s history, importance in plant biology, and interactions with phytohormones must all be understood to comprehend its physiological impacts on plant growth and development. This study examines how SNP influences seed germination, root growth, flowering duration, fruit development, and resistance to biotic and abiotic challenges to improve stress tolerance and crop productivity. Based on the literature review this study explored the molecular and pharmaceutical mechanisms of SNP-phytohormone, crosstalk affects, important signaling pathways, including calcium-dependent signaling and MAPK cascades. The requirement for tailored application strategies is highlighted by the fact that different plant species and genotypes react to SNP treatment differently depending on the context. This study also discussed the consequences of environmental and agricultural sustainability, emphasizing SNP’s potential to improve stress tolerance, pest control, and crop output. For sustainable, practical applications, it also underlines the necessity to handle obstacles and constraints such as concentration-dependent effects and potential environmental repercussions. Understanding the complex interactions between SNP and phytohormones provides doors for sustainable agriculture and biotechnology advancements. This comprehensive study offers encouraging possibilities for solving major issues in agriculture and environmental resilience by illuminating the molecular and physiological mechanisms.

Salinity is a major abiotic stress that limits plant growth and productivity. Role of silicon (Si) nutrition and arbuscular mycorrhiza (AM) in mitigating salt stress has gained importance in recent years. Legumes are sensitive to salinity and are considered low Si-accumulators. AM have been reported to increase Si uptake in mycorrhizal plants. However, little is known about the alleviative role of Si and/or AM in mitigating salt stress in Cicer arietinum L. (chickpea). Therefore, the present study was aimed to evaluate the individual and cumulative effect of Si and AM (Funneliformis mosseae) on nutrient status, growth and productivity of salt tolerant HC 3 and salt sensitive CSG 9505 genotypes of chickpea under salinity stress conditions. The genotypes were subjected to 0, 60, 80,100 mM NaCl and 0, 4 mM potassium silicate—K2SiO3 treatments in the presence and absence of AM fungi. The results indicated that the Si and AM treatments improve the endogenous nutrients profile, growth characteristics and yield attributes under salinity stress. AM was found to be more efficient in improving growth and productivity while Si was more beneficial in improving K+/Na+ ratio. Mycorrhization mediated significant improvement in Si uptake and as a result, Si supplementation along with mycorrhization reduced Na+ content significantly, improved growth, yield and nutrient uptake, arrested chlorophyll pigment damage and increased RUBISCO activity. HC 3 was more responsive to mycorrhization and Si nutrition than CSG 9505. The study will contribute to our understanding of Si and/or AM mediated salinity tolerance mechanism for developing chickpea genotypes resistance to salt stress.