Anatomical Observations on the Accumulation and Utilization of Storage Starch and Epidermis-related Development in Roots of Vigorous and Non-vigorous Satsuma Mandarin Trees from Early Winter to Early Summer.

Abstract

Accumulation and utilization of storage starch and epidermis-related development in roots of vigorous and non-vigorous satsuma mandarin (Citrus unshiu Marc. cv. Miyagawa Wase) were compared anatomically from early winter to early summer. Only a few starch grains were deposited in the cortex of the pioneer roots of both kinds of trees in December. In vigorous trees, the number of starch grains per cortical cell and the ratio of areas of starch grain to the area of cortex (area-ratio) increased considerably during January and February, attaining a maximum in March. Area-ratio gradually decreased from April to May ; by June, it approached zero as the starch grains almost disappeared. In contrast, the area-ratio in non-vigorous trees was unchanged from January to February and increased slightly in March. The area-ratio reached the highest level in April, followed by rapid reduction in May, as the starch grains disappeared in June. Neither the vigorous nor the non-vigorous trees contained starch grains in July. Fibrous roots on vigorous trees were filled with many starch grains up to April, then the grains disappeared completely in June ; whereas in non-vigorous trees starch grain depletion started in June but the grains persisted until July. The pioneer roots on vigorous trees had but one layer of phellogen cells beneath the epidermis in January. The periderm was distinct with the formation of phellem, phellogen, and phelloderm in March. Periderm formation in non-vigorous trees was initiated in March, and it continued slowly into April. Root hair and epidermal development was faster in roots of vigorous tree.