Hormonal Status in Wheat and Rice Seedlings under Anoxia

A comparative analysis of the effects of anoxia on growth, fresh weight gain, and phytohormones in wheat (Triticum aestivum L.) and rice (Oryza sativa L.) seedlings was performed. In both plant species, a total cessation of root growth occurred during the initial hours of anoxia. In an anaerobic environment, the fresh weight of wheat seedlings decreased. An increase in the shoot length and weight under the stress conditions was found only in rice seedlings. During the initial hours of anoxia, the level of free ABA in wheat and rice tissues increased manifold, and the accumulation of a free ABA form occurred at the expense of the hydrolysis of its bound forms. The IAA content in plant tissues also increased. In wheat, the accumulation of IAA was short, but in rice, a high hormone level was retained during the entire experiment, and, as a result, its concentration exceeded that of ABA. A level of cytokinins in the tissues of both plant species was affected by anoxia to a lesser extent than that of other phytohormones. This level somewhat decreased under anoxia similarly to the level in darkness under aeration. It is suggested that IAA accumulation in hypoxia-tolerant rice seedlings under anoxia favors maintenance of shoot growth and simultaneous inhibition of root growth. At the same time, in the hypoxia-sensitive wheat, an increase in the ABA level resulted in growth cessation.