James A. McWha

ytokinins and Changes in Their Activity During the Development of Grains of Wheat (Triticum aestivum L.)

Summary Changes in cytokinin content of developing wheat grains were investigated beginning at ear emergence. Cytokinin-like activity was barely detectable at ear emergence but had increased to 5.5 ng per pistil at pollination. The cytokinins have been identified tentatively as zeatin, zeatin riboside and their O-β-D-glucosides. Levels then increased rapidly until 4 d after anthesis after which an equally rapid loss occurred. No activity could be detected 21 d after ear emergence. All cytokinins were maximal 4 d after anthesis although the glucosides showed increased levels at an earlier developmental stage than either zeatin or zeatin riboside.

Wheat Research Institute, P. 0. Box 1489, Christchurch, New Zealand: Abscisic Acid and the Movement of Photosynthetic Assimilates Towards Developing Wheat (Triticum aestivum L.) Grains

Summary When abscisic acid (ABA) was injected into wheat grains, during their development, the movement of 14 CO 2 labelled photosynthetic assimilate towards the ear increased. However, when the ear was removed and replaced with lanolin containing ABA, translocation was inhibited.

Endogenous abscisic acid in lettuce fruits

Summary Abscisic acid has been extracted from lettuce fruits of two varieties, «Great Lakes« and «Arctic King«, and identified by a combination of methods including partitioning, chromatography, spectropolarimetry and gas chromatography-mass spectrometry. The abscisic acid present in the dry fruits of the two varieties has been determined quantitatively and in “Great Lakes” the levels decreased during germination.

Abscisic Acid and Wheat Leaf Senescence: The Effect of Pre-treating the Intact Plant

Summary The loss of chlorophyll from segments of wheat leaves was accelerated by incubation in a medium containing abscisic acid (ABA) at 10-5 M or 10-4 M. However, regular spraying of the intact plants with ABA prior to excision of the leaf segments, significantly reduced subsequent chlorophyll loss. The presence of ABA in the incubation medium again accelerated chlorophyll loss from pre-treated tissue but the effect was greatly reduced compared with plants not pretreated by spraying with ABA.

The Use of Light-Emitting Diodes (LEDs) as Green and Red/Far-Red Light Sources in Plant Physiology.

The use of green, red, and far-red light-emitting diodes (LEDs) as light sources for plant physiological studies is described. LED lamps have the advantage over conventional light sources in that they are lightweight, low cost, portable, easily constructed and, more important, do not require colour filters. Using LED lamps, red/far-red reversal of germination of Grand Rapids lettuce seeds was demonstrated and the effectiveness of a green LED safelight was compared with that of a conventional filtered safelight, using extension growth of photosensitive Avena fatua L. seedlings as an indicator. The green LEDs gave comparable performance to the conventional filter-type safelight. An infra-red LED light source was also evaluated.

A simple demonstration of CO2-fixation and acid production in CAM plants

This paper describes a simple class experiment to investigate the fixation of C02 in the dark and the unique diurnal rhythm of acid production in plants that exhibit Crassulacean Acid Metabolism. Suggestions for additional experiments are also included.