The Length and Number of Epidermal Cells in Petioles of Strawberry Plants as Affected by Photoperiod and Temperature during Vegetative and Resting Periods

Abstract

Strawberry plants (Fragaria ananassa Duch. cv. Donner) were transferred from an unheated plastic film greenhouse to a growth chamber controlled at 24°/22°C (day/night) under the conditions of a 16-hr photoperiod on 23 August, 23 October, and 23 November.
1. Petioles of plants transferred to the growth chamber on 23 August became longer at higher leaf positions. This is attributed to the increase in the number of epidermal cells per petiole length (cell number) ; concurrently, the mean length of those cells (cell length) decreased.
2. Petioles of plants transferred to the growth chamber on 23 October or 23 November also became longer at higher leaf positions, but their final length was shorter than that of the plants transferred to the growth chamber on 23 August.
3. Petioles of plants kept at 3°C in the dark for 42 days from 23 November and then transferred to the growth chamber became significantly longer than those of the plants transferred to the growth chamber on 23 November without chilling, irrespective of the positions of leaves. This increase in the petiole length of the first 3 leaves to elongate under the growth chamber conditions is mainly attributed to the increase in the cell length; the contribution by the number of cells increased remarkably at higher leaf positions than in these basal 3 leaves.
4. The length and the number of epidermal cells in petioles of strawberry plants during their growth and resting periods are supposed to change under the subsequent long-photoperiod and high-temperature conditions as follows:
(1) During the growth period, petioles at higher leaf positions elongate on account of the increase in the number of cells per unit length.
(2) As plants gradually enter the resting state during the fall season, the cell division of petioles developing in the crown is extremely inhibited under short-photoperiod and low-temperature conditions.
(3) During the rest period, chilling mainly preconditions petiolar cells to increase in length during the subsequent long-photoperiod and high-temperature conditions when the leaves approach emergence. However, the same chilling treatment promotes cell proliferation in petioles which are still in the differentiation stage.