AUTOLYSIS IN HERBACEOUS, DICOTYLEDONOUS PLANTS - EXPERIMENTAL MANIPULATION OF PITH AUTOLYSIS IN SEVERAL CULTIVATED SPECIES

Pith autolysis, a condition in which dicotyledonous herbaceous plants have a hollow stem, results from the autolysis of a plant's storage pith. Our central hypothesis concerning the aetiology of pith autolysis states that the carbon from the pith is transported to the growth regions of the plant and used at times when the plant cannot meet its carbon needs by photosynthesis alone. According to this hypothesis, accelerated growth should increase pith autolysis. We here provide supporting evidence for the central hypothesis. More pith autolysis was found in faster growing tomato varieties than in dwarf varieties. More pith autolysis was found in both beans and tomatoes treated with GA(3) than in controls. More pith autolysis was found in leggy bean plants grown in low light than in normal plants grown under normal light conditions. Pith autolysis decreased in both beans and tomatoes when mechanically perturbed or sprayed with paclobutrazol, both treatments that reduced growth. The stems of buckwheat plants that were flowering showed greater pith autolysis and therefore were more hollow than plants which were not flowering or which had the incipient flowers pinched off. This indicated that carbon from the storage pith may also be used in the formation of reproductive structures which require extra carbon. Also in support of the central hypothesis is the prevention of pith autolysis by the addition of extra carbon to the plant, in the form of an increased CO2 concentration of the surrounding air. (C) 1995 Annals of Botany Company