Response of Etiolated Pea Seedlings and Cotton to Ethylene Produced from L-methionine by Soil Microorganisms

The presence of a suitable substrate(s) in soil may release physiologically active concentration of a plant hormone ethylene (C2H4) as a result of microbial activity. We isolated three strains of fungi (Aspergillus clavatus, Penicillium commure and Thamridium elegans), from the maize rhizosphere soil, capable of producing C2H4 in the soil from L-methionine (10 mmol l). The plate and soil inoculation experiments conducted under controlled conditions revealed that the C2H4 released as a result of precursor (L-MET)-inoculum (fungi) interaction caused a classical “triple” response in etiolated pea seedlings (a significant reduction in seedling length and increase in stem diameter). The classical “triple” response was also observed in the etiolated pea seedlings grown in non-sterilized soil amended with L-MET (no inoculation). The application of Ag(I), an inhibitor of C2H4 action, partially eliminated the classical “triple” response in etiolated pea seedlings. A significant direct correlation (r = 0.910* to 0.997**) was found between classical “triple” response and [L-MET] or [C2H4 gas]. The results of pot trial conducted on cotton indicated that L-MET applied at 1.0 and 10.0 mg kg soil significantly increased the number of bolls (up to 45.5%), seed cotton weight (up to 35.7%), and root and shoot weight (up to 35.1 and 28.2%) over the unammended control. The results of this study imply that C2H4 production is a substrate-dependent biochemical process and application of small quantity of L-MET (1-10 mg kg soil) may affect plant growth.