Journal of Plant Growth Regulation

Borrichia frutescens (L.) DC., sea marigold, is a woody perennial shrub native to the Gulf and Atlantic coasts of North America and has potential as a landscape shrub or groundcover. This study assesses application rates of three commercially available plant growth regulators (PGRs) on B. frutescens during container production. In one experiment, plants were drenched with 0, 0.5, 1, 2, or 4 mg active ingredient (a.i.) pot−1 of uniconazole or 0, 5, 10, 20, or 40 mg a.i. pot−1 of paclobutrazol, and in a second experiment, plants were sprayed with solutions of either 0, 25, 50, 100, or 200 mg a.i. L−1 of uniconazole, 0, 50, 100, 200, or 400 mg a.i. L−1 of paclobutrazol, or 0, 2500, 5000, 10000, or 20000 mg a.i. L−1 of daminozide. Drench-applied paclobutrazol (40 mg a.i. pot−1) reduced shoot mass and root mass (52.9 and 48.5 %, respectively). Both paclobutrazol (40 mg a.i. pot−1) and uniconazole (2 mg a.i. pot−1) reduced leaf number by as much as 56.7 and 23.8 %, respectively. Height was reduced 54.9 % by paclobutrazol at 40 mg a.i. pot−1 and 34.9 % by uniconazole at 2 mg a.i. pot−1. Drench application of paclobutrazol and uniconazole reduced internode extension by 50.1 and 41.4 %, respectively. At the levels tested, daminozide, paclobutrazol, and uniconazole were generally ineffective at controlling growth when applied as a spray. Drench application of paclobutrazol or uniconazole can be used to control height during container production of B. frutescens, whereas spray application rates need to be tested at higher concentrations or multiple applications to achieve desired control.

Fullerenols are carbon nanoparticles that have been declared as free radical sponges. There is a need to take a prudent path toward its applications in various biological systems. For plants, polyhydroxy fullerenes can be beneficial nanozymes with the ability to scavenge all forms of reactive oxygen species produced within sub-cellular compartments. However, limited information is available regarding the role of these synthetic nano-antioxidants within plant biosystems. The unique chemistry of fullerenes makes them behave as nanozymes that can neutralize all reactive oxygen and nitrogen forms. This property can be utilized for oxidative stress tolerance among plants under stressful environments. Therefore, the knowledge of plant–fullerenol interactions is crucial. The present review describes molecular mechanisms regarding its effects at sub-cellular, cellular, and tissue levels of organization. In addition, the effects of various fullerenol derivatives on different plant species are also provided at length in this review to give insights regarding fullerenol-induced regulation of plant growth and crop protection.

The effects of sandy soil pH on the distribution of growth velocities and on cation concentrations and deposition rates in root growth zones of Zea mays L. seedlings were investigated. The pH values of the rooting medium varied between 4.2 and 8.6 in sand culture (70% saturated) without external supply of nutrients. At all pH values, densities (in μmoles per g fresh weight) of potassium, magnesium, and calcium increased toward the root tip. Lower pH in the medium increased calcium tissue density fivefold and magnesium density 1.7-fold, whereas the density of potassium, the overall elongation rate, and the growth velocity distribution did not show any significant pH dependence. Throughout the growth zone the deposition rates of the divalent cations, as calculated on the basis of the continuity equation, increased with lower pH. The data are consistent with the hypothesis that the effects of pH on the cation deposition rates are due to the increase in the divalent cation concentration of the soil solution at low pH and that the abundant uronic acid residues of the young walls of the meristem provide a reservoir of storage capacity for Ca and Mg under conditions of low nutrient availability.

The effects of cytokinins on the in vitro growth of the roots of Arabidopsis thaliana seedlings were examined. Root growth was inhibited in a manner dependent upon the type of cytokinin compound, the cytokinin concentration, the Arabidopsis genotype, and the duration of exposure to cytokinin. For the cytokinins N 6-benzyladenine (BA), isopentenyl adenine (iP), or dihydrozeatin (DHZ), the concentration required for 50% root growth inhibition differed for each cytokinin and in each of three Arabidopsis genotypes tested. iP was the most active cytokinin in inhibiting the root growth of the Ler-0 genotype, whereas iP and BA had equal activity when tested with the Col-2 and Columbia genotypes. DHZ had the lowest activity of the three cytokinins tested in all three genotypes. A brief 1-day exposure of seeds to a root-inhibiting concentration of BA increased root growth compared with seedlings grown without BA; exposure to BA for 3–6 days inhibited root growth. BA metabolism was evaluated after 6 h and 1, 3, and 6 days in Columbia seedlings. BA, N 6-benzyladenosine (BAR), and N 6-benzyladenosine-5′-monophosphate (BAMP) decreased with time, whereas N 6-benzyladenine-7-β-d-glucopyranoside (BA-7-G) and N 6-benzyladenine-9-β-d-glucopyranoside (BA-9-G) accumulated in the growing seedlings. Seven aromatic cytokinins were compared at 5 μm for their effect on Col-3 root growth. BA, BAR, N 6-(m-hydroxybenzylamino)adenine, and N 6-(o-hydroxybenzylamino)adenine were highly effective in inhibiting root growth, whereas N 6-(p-hydroxybenzylamino)adenine produced only a slight decrease in root growth. BA-7-G and BA-9-G did not affect root growth.

Salinity causes osmotic stress and negatively impacts plant growth and productivity. Proline is one of the most important osmoprotectants synthesized under stressed conditions. Accumulation of free proline occurs due to enhanced biosynthesis and repressed degradation, and both processes are controlled by feedback regulatory mechanisms. Arbuscular mycorrhizal (AM) fungi are considered to be bioameliorators of salinity stress due to their wide-ranging presence in contaminated soils and their role in modulation of biochemical processes. Chickpea is considered sensitive to salinity. However, reports on AM-induced osmoprotection through regulation of proline biosynthesis in chickpea genotypes are scant. The present study investigated the influence of AM symbiosis on proline metabolism in two chickpea (Cicer arietinum L.) genotypes (PBG-5 and CSG-9505) under salt stress and correlated the same with sodium (Na+) ion uptake. Salinity reduced plant biomass (roots and shoots), with roots being more negatively affected than shoots. Mycorrhizal colonization with Glomus mosseae was much stronger in PBG-5 and was correlated with reduced Na+ ion uptake and higher growth when compared with CSG-9505 under stressed and unstressed conditions. Mycorrhizal symbiosis with chickpea roots boosted proline biosynthesis by significantly increasing pyrroline-5-carboxylate synthetase (P-5-CS) and glutamate dehydrogenase (GDH) activities with a concomitant decline in proline dehydrogenase (ProDH) activity under salt stress. The enhancement of the activity of these enzymes was higher in PBG-5 than in CSG-9505 and could be directly correlated with the percent mycorrhizal colonization and Na+ uptake. The study indicated a strong role of AM symbiosis in enhancing stress tolerance in chickpea by significantly modulating proline metabolism and Na+ uptake.

Nanotechnology can be effectively used in agriculture to improve crop production. Biosynthesized nanoparticles can enhance the growth and yield of several crops. In this work, we examine the effect of green synthesized silver nanoparticles from Pongamia pinnata (L.) Pierre leaf extract on the germination and growth of Black gram (Vigna mungo (L.) Hepper). Upon treatment with biosynthesized silver nanoparticles, we found a 22% increase in seed germination and a 36% enhancement in seedling growth. Further, pot experiments revealed a significant increase in root length (33%), pod weight (21%) and grain weight (26%). A significant increase in phenolics (20%) and carbohydrates (17%) was also observed. Assessment of the antioxidative enzymes revealed a significant increase in catalase activity (9%), thus indicating a reduced oxidative stress and associated damage. The results suggest that biocompatibility of the synthesized nanoparticles and efficient ROS scavenging mechanisms together play an important role in exhibiting an overall positive effect on germination, growth and development of Black gram (Vigna mungo (L.) Hepper). The evidence also suggests that Pongamia pinnata (L.) Pierre may be a good source for the biosynthesis of nanoparticles and use as a plant growth enhancer.

Botrytis cinerea Pers.:Fr. is an important pathogen in tomato plants that causes stem rot of tomatoes grown indoors for an extended period. MicroRNAs (miRNAs) have recently been reported as a class of gene expression regulators linked to stress responses; however, data on the role of miRNAs in plant responses to biotic stresses are still limited. In this study, three Botrytis stress-responsive miRNAs were identified using microarray analysis and the effects of Botrytis infection were surveyed in tomatoes. Two downregulated miRNAs and one upregulated miRNA were detected. These stress-responsive miRNAs regulated metabolic, morphological, and physiological adaptations of tomato seedlings at the post-transcriptional level. The presence of stress-related elements in the miRNA promoter regions further supports our results. These findings extend the current view about miRNAs as ubiquitous regulators under stress conditions.

Climate change leads to frequent alterations in environmental factors with a reciprocal impact on crop productivity. Over the last few decades, various approaches have been used for producing more stress-tolerant and climate-flexible crops. Genetic engineering is one of the approaches used to modify multiple characters or to improve more than one agronomic trait in plants. These instances simultaneously demand simultaneous genetic manipulation of multiple genes, necessitating stacking or pyramiding of multiple genes as compared to single-gene manipulations, and the genetic engineering of plants using multiple genes is technically challenging. In the last two decades, considerable progress has been made with respect to the development and application of the methods for gene pyramiding in transgenic context. The conventional methods of gene stacking include the crossing of individual transgenic plants, co-transformation using multiple plant expression constructs, transformation with single constructs carrying multiple transgenes as well as with the constructs carrying polycistronic transgenes. These methods have been instrumental for gene stacking in several commercialized crops. The tools of targeted genome editing (ZFN, TALEN, and CRISPR) that carry out precise genetic modifications, have opened new avenues in the area of crop biotechnology for defending plants against various stresses. The present review covers the current status of biotechnological techniques used to combat biotic and abiotic stresses in crop plants and describes multiple associated challenges.