A detailed study has been made of the morphology of the spring.barley apex from shortly after germination to shortly before heading. The effects of 8-and 24-hr light periods and three levels of soil-moisture tension were examined with reference to the total number of primordia initiated on the main stem, the length of the apex, and the rate of spikelet development.For the environmental conditions explored it was found that the initiation of double ridges occurred when the apex was a particular length (0' 45 mm), and that the initiation of internode elongation, the appearance of stamen initials on the most advanced spikelet, and the cessation of primordia formation occurred concurrently.

The effects of soil moisture stress on tillering, stem elongation, and grain yield of barley (cv. Prior) have been studied by subjecting the plants to periods of stress at different stages of development. Soil moisture stress treatments consisted of repeated short cycles of stress, single short cycles (both in large pots), or single long cycles (in large lysimeters). The data collected support the contention that the organ which is growing most rapidly at the time of a stress is the one most affected. Grain numbers per ear were seriously affected by stress occurring prior to anthesis, an effect probably associated with the process of spikelet initiation and, later, with the formation of the gametes. Grain size, on the other hand, was reduced more by stress at anthesis and shortly after. Elongation of the internodes was reduced mostly by stress at or just before earing, and was less seriously affected by earlier or later stress. Tillering, although being suppressed during a drought cycle, was actually stimulated upon rewatering. The effect was greater the earlier the period of stress, and was probably related to nutrient uptake and distribution within the plant.

No abstract

No change in the total β-amylase activity, attributable to the presence of 10-6 M gibberellic acid (GA3) in the incubation medium, was found in freshly harvested, de-embryonated, immature (11-38 days post-anthesis) caryopses of wheat. Significant amounts of GA3-induced α-amylase activity was found in 26-h incubates of similar caryopses which had been allowed to dry out either in the ear or detached from the ear. After 10 days of storage of detached immature caryopses in air of 99-100% relative humidity, de-embryonated half-caryopses responded to applied GA3 by producing α-amylase. More α-amylase was found in 26-h incubates if detached caryopses dried out slowly, but rapid desiccation led to little or no α-amylase being produced in the presence of GA3. Caryopses taken from ears cultured on 0.4 or 4% sucrose for 10 days did not respond to applied GA3 whereas those from ears cultured on water did respond, although the amount produced in 26-h incubates was not as large as those from slowly dried ears. Development of the ability to respond to GA3 by increasing α-amylase activity depended on the duration of desiccation or isolation from the plant. Changes in metabolism emanating from the interruption to the supply of sucrose to the caryopsis may be involved in the development of the ability of the aleurone to respond to GA3.

When endosperm halves taken from batches of Himalaya barley grown in the United Kingdom and in various years in the U.S.A. and from Clipper barley grown in South Australia were incubated in either the presence or absence of gibberellic acid, variability in the production of α-amylase was found between batches. Samples from selected batches were grown in glasshouse conditions in winter and in summer. The amount of α-amylase produced in either the presence or absence of gibberellic acid depended on the environmental conditions operating during grain filling and on drying temperature of ears harvested late in grain filling. Two reponse-types of endosperm were distinguished: type A had a strict requirement for exogenous gibberellic acid, whereas type B did not. Himalaya ears grown at temperatures greater than 20°C in controlled environment conditions produced type B endosperm. Similar kinetics of production of °-amylase were found for both types. The notion that the high production of °-amylase in the absence of exogenous gibberellic acid by type B endosperm was induced by high amounts of endogenous gibberellin-like materials was not supported by experiments where either endosperm halves or stacks of endosperm slices of both types were incubated together.