Cytokinin Production by Azospirillum brasilense Contributes to Increase in Growth, Yield, Antioxidant, and Physiological Systems of Wheat (Triticum aestivum L.)

Abstract

Plant growth-promoting rhizobacteria are known to associate with several cereal crops. The rhizobacterium exerts its function by synthesizing diverse arrays of phytohormones, such as cytokinin (Ck). However, it is difficult to determine the plant growth promotion when a bacterium produces many different kinds of phytohormones. Therefore, to assess the involvement of Ck in growth promotion and activation of antioxidant and physiological systems, we set up this experiment. Wheat seeds (Triticum aestivum L.) were inoculated with Azospirillum brasilense RA−17 (which produces zeatin type Ck) and RA−18 (which failed to produce Ck). Results showed that seed inoculation with RA−17 significantly improved growth and yield-related parameters compared with RA−18. The activity of enzymes, proline contents, and endogenous hormonal levels in wheat kernels were improved considerably with RA−17 than with RA−18. Strain RA−17 enhanced grain assimilation more than strain RA−18 resulting in a higher crop yield. These results suggest that microbial Ck production may be necessary for stimulating plant growth promotion and activating antioxidant and physiological systems in wheat.

Exogenous Kinetin Modulates ROS Homeostasis to Affect Heat Tolerance in Rice Seedlings

“…Thus, we speculate that exogenous KT treatment may enhance the heat tolerance of rice by enhancing CK response activity. Increased endogenous CK concentration in tobacco and bryophytes leads to increased antioxidant system activity and upregulation of heat shock protein expression [ 45 , 46 ]. Consistent with this result, the transcript levels of heat response genes OsHSP70 , OsHSP90 , and OsHsfA2d were significantly upregulated in the KT group compared with the control group under heat stress, consistent with the trend of increasing CK concentration ( Figure 5 A–C).…”

Deciphering the potential of a plant growth promoting endophyte Rhizobium sp. WYJ-E13, and functional annotation of the genes involved in the metabolic pathway

“…Besides, cytokinins also play a significant role in plant growth promotion ( Gao et al, 2022 ). For example, cytokinin production by Azospirillum brasilense contributed to increase in growth, yield, antioxidant, and physiological systems of wheat ( Zaheer et al, 2022 ). Expectedly, a gene chr_1443 was annotated to possess cytokinin dehydrogenase activity ( Table 4 ).…”

The role of plant growth promoting rhizobacteria in plant drought stress responses

“…Interestingly, inoculation of plants with PGPR can also modulate plant hormone synthesis to promote plant tolerance to drought stress. PGPR produce several external plant growth regulators such as auxin or IAA [ 74 ], CK [ 75 ], ET [ 76 ], ABA [ 77 ], SA [ 78 ], and JA [ 79 ]. The phytohormonal pathways can engage in a network of interconnected responses to help plants cope with drought stress.…”

“…Bacillus subtilis producing CK increased the endogenous content of CK and promoted lettuce development under drought conditions [ 98 ]. CK-producing Bacillus subtilis had a favorable effect on Platycladus orientalis (oriental thuja) plant development under drought stress [ 75 ]. In this study, drought stress alone reduced shoot CK levels by 39.14%, but inoculation with cytokinin-producing Bacillus subtilis reduced the inoculated stressed plants’ CK by only 10.22%.…”

“…Phyllobacterium brassicacearum STM196 beneficial strain increased ABA content in inoculated Arabidopsis plants, which reduced leaf transpiration and improved osmotic stress tolerance in the plants [ 119 ]. Inoculation of Platycladus orientalis seedlings with cytokinin-producing Bacillus subtilis strain resulted in higher ABA levels in shoots and increased stomatal conductance, conferring resistance to drought stress [ 75 ]. Treating mustard seedling with a Bacillus marisflavi CRDT-EB-1 strain that produced ABA precursors, xanthoxin and xanthoxic acid, induced stomata closure and caused the plants to be drought tolerant [ 120 ].…”