Photoperiod, Photon Exposure and the Growth and Sucrose Content of the Wheat Shoot Apex

Abstract

Wheat cv. Warimba plants were grown in a controlled environment in either a long (16 h) or short (8 h) photoperiod. When the apices reached the stage of floret initiation in the long photoperiod, some plants were transferred to the short photoperiod at the same photon irradiance and others to a lower photon irradiance in the long photoperiod. The plants growing initially in the short photoperiod were transferred at a slightly earlier stage of development (lemma initiation) to either the high photon irradiance-long photoperiod environment or to the short photoperiod at the lower photon irradiance. Apices were divided into upper and lower portions and their dry weights and soluble sugar contents were determined. Sucrose alone was found in most of the apices with trace amounts of glucose and fructose being found late in development in the apices of plants growing in the long photoperiod. There was always a higher sucrose concentration in the lower portion of the apex than in the upper. Transfer to a low photon irradiance reduced apical sucrose content, sucrose initially disappearing completely from the upper region of the apices growing in the long photoperiod. There was some subsequent recovery, however. Transfer to the alternative photoperiod also reduced apical sucrose content, although not as severely.