Pith Autolysis in Herbaceous, Dicotyledonous Plants: Experimental Manipulation of Pith Autolysis in Several Cultivated Species

Pith autolysis, a condition in which dicotyledonous herbaceousplants have a hollow stem, results from the autolysis of a plant'sstorage pith. Our central hypothesis concerning the aetiologyof pith autolysis states that the carbon from the pith is transportedto the growth regions of the plant and used at times when theplant cannot meet its carbon needs by photosynthesis alone.According to this hypothesis, accelerated growth should increasepith autolysis. We here provide supporting evidence for thecentral hypothesis. More pith autolysis was found in fastergrowing tomato varieties than in dwarf varieties. More pithautolysis was found in both beans and tomatoes treated withGA₃ than in controls. More pith autolysis was found in leggybean plants grown in low light than in normal plants grown undernormal light conditions. Pith autolysis decreased in both beansand tomatoes when mechanically perturbed or sprayed with paclobutrazol,both treatments that reduced growth. The stems of buckwheatplants that were flowering showed greater pith autolysis andtherefore were more hollow than plants which were not floweringor which had the incipient flowers pinched off. This indicatedthat carbon from the storage pith may also be used in the formationof reproductive structures which require extra carbon. Alsoin support of the central hypothesis is the prevention of pithautolysis by the addition of extra carbon to the plant, in theform of an increased CO₂ concentration of the surrounding air.Copyright1995, 1999 Academic Press Bean, tomato, buckwheat, pith autolysis, CO₂, GA, thigmomorphogenesis, packobutrazol