Transport of Materials from the Cotyledons during Germination of Seeds of the Garden Pea (Pisum sativumL.)

Abstract

The transport of total dry matter, nitrogen, phosphorus, sulphur, potassium, and calcium from the cotyledons into the developing axis of young pea (Pisum sativum L.) seedlings has been studied under a variety of growth conditions. It is shown that the duration of transport increased when the plants were grown in distilled water, or in the dark, or upon removal of the shoot ; all these treatments delayed senescence of the cotyledons. On the other hand, the rate of transport was increased by treatments, such as the supply of calcium and phosphate in the medium, or darkness, which stimulate growth of the axis. Treatment of the seeds before germination with gibberellic acid (GA3) did not affect the movement of materials from the cotyledons although it changed the pattern of growth of the axis. After the first week of germination the relationship between the amounts of total dry matter, nitrogen, phosphorus, sulphur, and potassium transferred to the axis from the cotyledons in the intact plant remained approximately constant irrespective of the conditions of growth. It is proposed that the ratio in which the individual elements are transported is determined by the proportions in which they are released by the storage cells. Deviation from this ratio during the first week of germination, and over a longer period in deshooted plants is attributed to competition for the available nutrients between actively metabolizing cells in the cotyledons and axis. It is demonstrated by steam-girdling that movement of materials from the cotyledons into the shoot probably occurs via the phloem. Calcium is mobile in the phloem during the early stages of germination, possibly because the amount of free calcium in the cotyledons is high.