THE EFFECTS OF PHOTOPERIOD AND TREATMENT WITH GIBBERELLIC ACID ON THE CONCENTRATION OF SOLUBLE CARBOHYDRATES IN THE SHOOT APEX OF SPRING BARLEY

Abstract

Barley plants (Hordeum vulgare L. cv. Clipper) were grown in controlled environment rooms for varying periods. The total soluble carbohydrate concentration was determined for stem apices over the period of early ear development using the p‐hydroxybenzoic acid hydrazide method. Concentration of soluble carbohydrates rose during the photoperiod and was lower in the apices of plants subjected to shade. It also increased as the ear enlarged, irrespective of photoperiod. In 8 h photoperiods plants initiated many more spikelets, but at a lower rate, compared to those grown in 16 h days. Apices of plants grown in 8 h days showed a lower relative growth rate, but despite this at the end of spikelet initiation concentration of soluble carbohydrates was about 30% higher than for apices from plants in 16 h photoperiods. Where plants were grown in 8 h high intensity light followed by 8 h low intensity light soluble carbohydrate content was slightly more than in the apices of plants kept throughout 16 h in high intensity light. Treatment of plants grown in 8 h photoperiods with gibberellic acid accelerated the rates of initiation and development of spikelets. Treatment caused a substantial but ephemeral increase in soluble carbohydrate content, although by the time that spikelet initiation ceased the concentration was similar in control and treated plants. It is concluded that total soluble carbohydrate concentration in the apex is not related to either rate of initiation or rate of development of spikelets. It is suggested that rate of utilisation of available soluble carbohydrate is subject to photoperiodic control and restricts growth and development of the ear. Copyright © 1986, Wiley Blackwell. All rights reserved