Hormone‐like effect of vascular tissue on starch accumulation in stem explants of kale, Brassica oleracea

Abstract

Explants of stem pith of kale (Brassica oleracea L. var. medullosa cv. Krasa), cultured for several days on agar medium containing sucrose, accumulate starch. Application of streptomycin, 5‐fluorouracil and other inhibitors indicates that starch accumulation depends on protein synthesis on 80 S ribosomes. If explants derived from plants grown under natural long‐day conditions contained vascular tissue, including cambium, in addition to pith parenchyma, the amount of starch formed in the pith tissue increased up to seven fold when compared with explants without vascular tissue. Similar increase of starch content as caused by vascular tissue was achieved by the addition of kinetin or trans‐zeatin (10 μ) in the presence of 5 μ indole‐3‐acetic acid or 1‐naphthaleneacetic acid. A further three‐fold increase in starch accumulation could be achieved by application of cytokinin and auxin to explants containing vascular tissue. When explants were derived from plants grown under natural short‐day conditions cytokinins and auxins had little or no effect, but vascular tissue enhanced starch formation significantly. The spreading of starch inducing stimulus from vascular tissue (probably from its meristematic region) to the pith parenchyma up to a distance of at least 20 mm was demonstrated. It was concluded that a hormone‐like factor other than cytokinin and auxin was involved in the stimulatory action of vascular tissue. The effects of this factor on protein accumulation and growth in the explants and its possible production by meristematic tissues in vivo are discussed.