The Difference Of Water-deficit Induced ABA Biosynthesis In Root And Leaf Of Zea Maize Seeding

Drought is one of the primary adverse environmental factors. Unlike animals, plants cannot actively escape the damages caused by drought stress. However, plants have evolved many mechanisms to actively cope with the drought stress, from nophological to molecular levels. One of the most important mechanisms is to biosynthesize and to accumulate rapidly and significantly ABA upon exposure to drought stress. The drought-induced ABA can adjust stomatal movement and stimulate root growth and water uptake, and thus keep the plant body in a balance of water status. A lot of evidences have showed that drought stress can significantly induce ABA accumulation both in roots and in leaves. However, great differences were observed in the amount of ABA accumulated and in the sensitivity to drought stress in terms of ABA biosynthesis between rootas and leaves. At present, we know little about the causes of these differences. In the present study, we, using maize as experimental material, firstly studied the effects of soil drought on physiological characters of maize, and then explored the possible causes in the drought-induced accumulation of ABA in roots and in leaves. The main results are as follows:1. At the early stage of soil drying, leaf water potential, stomatal conductance and photosynthetic rate of maize leaves decreased, and the related chlorophyll fluorescence parameters were not affected under the same conditions. However, along with the progress of soil drying, chlorophyll fluorescence parameters were also affected as well as leaf water potential, stomatal conductance and photosynthetic rate of maize leaves. On the contrary, leaf and root ABA accumulated significantly upon exposure to soil drying stress. Correlative analysis showed that the ABA contents in roots and leaves were negatively correlated to the leaf water potential, stomatal conductance and photosynthetic rate.2. Results based on the water loss rate from the detached leaves and roots showed that leaves did not significantly accumulate ABA before leaf water loss rate rached 3.47%, whereas, when the water loss rate was more than 16.2%, the roots begain to significantly accumulate ABA. Correspondingly, the leaf and root water potential were -0.538 MPa and -0.24MPa, respectively.3. RT-PCR indicated that drought significantly stimulated the expression of VP14 gene, a gene encoding key enzyme in ABA biosynthesis pathway, NCED, in leaves, but not in roots, Whereas, the expression of root AO1 gene was up-regulated by drought stress.