ENVIRONMENTAL CONTROL . . . . . . . . . . . . . . . . .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Genetics of Sensitivity to Environmental Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Control by Day Length . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Control of floral evocation and morphogenesis

The control of floral evocation and morphogenesis

Yield increases in temperate cereals have been associated with increases in grain number. An experiment was conducted to investigate whether altering the duration of the stem elongation period in wheat and barley increases floret fertility and thereby grain number. A photoperiod-responsive spring wheat (UQ189) and spring barley (Arapiles) were grown in a naturally lit phytotron. Plants were grown at constant (9, 13 and 19 h) and reciprocally interchanged photoperiod [at terminal spikelet (TS, wheat) or triple mound (TM, barley)] to alter the duration of the stem elongation period. An increased duration of the late reproductive phase from TS to heading in wheat resulted in more fertile florets per spike. A similar relationship was observed in barley but only for a limited range of duration of the stem elongation period. Shorter photoperiods reduced the rate of floret development and extended the time to reach the fertile floret stage. The fact that the duration of the late reproductive phase during which the spike and stem competing for assimilates was associated with the number of fertile florets per spike suggests that extending the stem elongation period in cereals could be a way to reduce assimilate competition and thereby increase the number of fertile florets and grain yield.

Duration of the stem elongation period influences the number of fertile florets in wheat and barley.

Comprehensive studies in grasses show that gibberellins (GAs) play a role as a florigen. For Lolium temulentum, which flowers in response to a single long day (LD), GAs are a transmitted signal, their content increasing in the leaf early in the LD and then, hours later, at the shoot apex. There is a continuous trail of evidence of hormonal action of these GAs for L. temulentum and support for a similar role in the flowering of other LD-responsive temperate grasses and cereals. A characteristic of the initial flowering responses of grasses and cereals is their limited stem elongation. Interestingly, it is GAs with low effectiveness for stem elongation, GA5 and GA6, that reach the shoot apex and, structurally, are probably not degraded by 2-oxidase enzymes. By contrast, GA1 and GA4 cause stem elongation, may be inactive for floral evocation, and do not reach the vegetative shoot apex apparently because of susceptibility to degradation. However, GA4 can be florally active if protected against 2-oxidases either structurally or by using a 2-oxidase inhibitor. Later in inflorescence development, GA1 and GA4 can be detected at the shoot apex and are florally active if applied. The 2-oxidase restricting accessibility to the apex has probably declined at this time so there is a second florigenic, LD-regulated GA action. A growing body of molecular evidence supporting these actions of GA may provide a future basis for manipulating flowering of grasses and cereals.

Gibberellins and Flowering of Grasses and Cereals: Prizing Open the Lid of the “Florigen” Black Box

The information on barley genes and chromosomes assembled consists of: {fx123-1}

/pdf/barley-genes-and-chromosomes-59mk1y6f19.pdf

Joan E. Cottrell

Papers

The Effects of Daylength and Treatment with Gibberellic Acid on Spikelet Initiation and Development in Clipper Barley

Development of the apical dome of barley in response to treatment with gibberellic acid

Early Growth of the Developing Ear of Spring Barley

The Effect of Application of Gibberellic Acid on Vegetative and Apical Development of nutans and erectum Barleys