EFFECT OF INHIBITORS OF ETHYLENE BIOSYNTHESIS AND ACTION, AS WELL AS CALCIUM AND MAGNESIUM ON ROSE SHOOT ROOTING, SHOOT-TIP NECROSIS AND LEAF SENESCENCE IN-VITRO

Microcuttings of easy-to-root dwarf rose cv. Starina, showing early sy mptoms of leaf senescence and shoot-tip necrosis in rooting stage, wer e chosen for the study. The effects of inhibitors of ethylene biosynth esis (AOA, AIB) and action (AgNO3), Ca2+ and Mg2+ were studied in rela tion to rooting, leaf senescence and shoot-tip necrosis. The effects o f these substances were examined with respect to IAA presence in a med ium, which stimulated leaf yellowing and shoot-tip necrosis. AOA stron gly inhibited rooting of microcuttings, but did not affect ethylene bi osynthesis. AIB at 250 mg.l(-1) and AgNO3 2.5 mg.l(-1) in the presence of IAA did not affect rooting but effectivity prevented leaf senescen ce. Ca2+ alone or combined with Mg at raised concentration, or an ethy lene action inhibitor Ag+, reduced shoot-tip necrosis in microcuttings treated with IAA. Addition of Ag+ to IAA medium drastically increased ethylene production by the shoots. Interaction between endogenous lev els of auxin, ethylene and calcium in relation to rooting, shoot-tip n ecrosis and leaf senescence was discussed. Ethylene could enhance tiss ue sensitivity to auxin. Moreover, the tissue of rose shoots is very s ensitive in the in vitro condition on standard medium because of the c alcium deficiency. Thus, the raised Ca/Mg level counteracted shoot-tip necrosis through enhancing cell membrane and wall resistance to ethyl ene and IAA.