Effect of Water Loss on Germination Ability of Maize (Zea mays L.) Pollen

The correlation between water content and viability of maizepollen grains was studied on the basis of the germination abilityof pollen from a single cross hybrid. There was found to beclose correlation between viability of the grains and theirtolerance to desiccation. Most of the pollen grains in the hybridexamined survived a reduction by almost 50 per cent of the originalwater content without loss of normal function. With water lossgreater than this, less vigorous pollen grains died or losttheir ability to form pollen tubes. Consequently, when pollinationwas carried out using pollen with a water content reduced bymore than 50 per cent, only the most tolerant pollen grainssurvived to take part in the competition which precedes fertilization.Dry pollen grains required a longer period to establish adhesionto the stigma surface and to initiate pollen tubes than pollengrains with higher water content, but otherwise their behaviourwas normal. If more than 80 per cent of the original water contentwas lost, disturbances occurred in the physiology of the grainssurviving the treatment. This was exhibited as death or a reductionin rate of pollen tube growth. Drying of pollen by an amount which does not irreversibly damagethe more tolerant grains could possibly be used as a means ofpollen selection. Zea mays L., maize, pollen viability, pollen treatment, dehydration, pollen tube     

Micro‐particle‐induced X‐ray emission mapping of elemental distribution in roots of a Mediterranean‐type sclerophyll,Agathosma betulina (Berg.) Pillans,colonized by Cryptococcus laurentii

The role of rhizosphere yeasts as plant nutrient‐scavenging microsymbionts in resource‐limited Mediterranean‐type heathlands is unknown. This study, therefore, focused on quantitative elemental distribution within the roots of a medicinal sclerophyll, Agathosma betulina (Berg.) Pillans, grown under nutrient‐poor conditions, and colonized by Cryptococcus laurentii. Micro‐particle‐induced X‐ray emission (PIXE) was used to assess quantitative elemental distribution within the roots of A. betulina inoculated with viable C. laurentii, as well as within roots of control plants that received autoclaved yeast. To aid in the interpretation of heterogeneous elemental distribution patterns, apoplastic barriers (Casparian bands) in root tissues were located using fluorescence microscopy. In addition, root cross‐sections were examined for endophytic C. laurentii using light and transmission electron microscopy (TEM). The average concentrations of P, Fe and Mn were significantly (P < 0.05) higher in roots of yeast‐inoculated plants, compared to control plants. Casparian bands were observed in the exodermal cells of both treatments, and the presence of these bands was correlated with elemental enrichment in the epi/exodermal‐outer cortical tissues. Light and TEM micrographs revealed that the yeast was not a root endophyte. This is the first report describing the role of a soil yeast as a plant nutrient‐scavenging microsymbiont.     

Fertility of Deep-frozen Maize (Zea mays L.) Pollen

On average, 50 per cent of maize pollen grains can be kept viableand almost 30 per cent remain fertile for up to a year whenthe water content on a fresh weight basis is reduced to about30 per cent of the original and the pollen is stored at –76or –196 °C. Over this period no significant differencewas found between storage at either temperature. Zea mays L., maize, pollen, fertility, viability