Study On Programmed Cell Death In M.hupehensis And M.sieversii Seedlings Under Drought

Two Malus plants ( M.hupehensis and M.sieversii seedlings ) were treated with polyethylene glycol (PEG6000) . It indicated that drought stress can induce programmed cell death of the two Malus by cytobiological, physiological, biochemistry, and immunochemical mechanism. The results are as follows:1. The changes of morphosis of nucleus, mitochondrion and chloroplast in leaves of sieversii generally were ealrier than hupehensis under drought stress. The changes of chromatin condensed at the periphery of nuclear and the outer membrane of mitochondrion and chloroplast in leaves of sieversii were greater than that of hupehensis. The changes and the extension of organelle morphosis in spongy mesophylls were earlier than in palisade parenchymas. The changes of morphosis of nucleus, mitochondrion and Golgi body in cortical cells were earlier than in pericycle cells. In the same Malus, the changes of organelle morphosis in roots were ealier than in leaves. And changes in roots were bigger than in leaves. The observation of cellular ultrastructure can be used to identify programmed cell death as alternative method.2. The contents of DNA, RNA and protein in leaves of sieversii decreased slower than hupehensis treated with 20% PEG 6000. The relative conductivity in leaves of sieversii increased slower than hupehensis. In the experiment of dying reaction with 0.1%NBT, the time of dying in leaves of sieversii was longer than hupehensis. Leaves of M.hupehensis wilted stronger than that of M.sieversii under drought stress. By comprehensive analysis, that there was programmed cell death during leaves senescence in Malus can be deduced.3. From the results of Southern blot, we can conclude that the DNA degrade was increasing with treated time. DNA Ladder about 180bp appeared in roots and leaves of M.hupehensis and M.hupehensis These results showed that is the feasible biochemistry parameter to identify fruit plants' programmed cell death in the earlier phase. Caspase-3 was checked in leaves in Malus with western blot. This phenomenon proved that Caspases participated in programmed cell death induced by drought and existed in leaves in Malus.Therefore the defense mechanism in M.sieversii is stronger than M.hupehensis. PCD appeared in M.sieversii earlier than M.hupehensis under drought stress.