Bruce G. Sutton

Effects of chilling on male gametophyte development in rice

Chilling during male gametophyte development in rice inhibits development of microspores, causing male sterility. Changes in cellular ultrastructure that have been exposed to mild chilling include microspores with poor pollen wall formation, abnormal vacuolation and hypertrophy of the tapetum and unusual starch accumulation in the plastids of the endothecium in post‐meiotic anthers. Anthers observed during tetrad release also have callose (1,3‐β‐glucan) wall abnormalities as shown by immunocytochemical labelling. Expression of rice anther specific monosaccharide transporter (OsMST8) is greatly affected by chilling treatment. Perturbed carbohydrate metabolism, which is particularly triggered by repressed genes OsINV4 and OsMST8 during chilling, causes unusual starch storage in the endothecium and this also contributes to other symptoms such as vacuolation and poor microspore wall formation. Premature callose breakdown apparently restricts the basic framework of the future pollen wall. Vacuolation and hypertrophy are also symptoms of osmotic imbalance triggered by the reabsorption of callose breakdown products due to absence of OsMST8 activity.

Cellular organisation in meiotic and early post-meiotic rice anthers

We have used fluorescent, confocal laser and transmission electron microscopy (TEM) to examine cellular organisations, including callose (1,3‐β‐glucan) behaviour, in meiotic and early post‐meiotic rice anthers. These features are critical for pollen formation and provide information to better understand pollen sterility caused by abiotic stress in rice and other monocotyledonous species. Among organelles during meiosis, abundant plastids, mitochondria and nuclei of the anther cells show distinctive features. Chloroplasts in the endothecium store starch and indicate a potential for photosynthetic activity. During meiosis, the middle layer cells are markedly compressed and at the tetrad stage are either vacuolated or filled with degenerating electron‐opaque organelles. Viable mitochondria, stained with Rhodamine 123, are seen in the endothecium and tapetum, but the mitochondria in the middle layer are not stained during meiosis. The radial walls of the tapetum are disorganised and degenerating, indicating the formation of a syncytium; pro‐orbicules are located at the locular walls at the tetrad stage. Immunohistochemical studies show that the sporogenous cells are entirely enveloped by a thick callosic layer at early meiosis. Cell plate callose was assembled in a plane between the dyad cells. In the tetrads, however, callose formed only at the centre, showing that the tetrad microspores are not enveloped but separated by callose walls. Thick, undulating electron‐opaque walls around the tetrads indicate the beginning of exinous microspore wall differentiation.

Chilling to zero degrees disrupts pollen formation but not meiotic microtubule arrays in Triticum aestivum L.

Throughout the wheat-growing regions of Australia, chilling temperatures below 2 °C occur periodically on consecutive nights during the period of floral development in spring wheat (Triticum aestivum L.). In this study, wheat plants showed significant reductions in fertility when exposed to prolonged chilling temperatures in controlled environment experiments. Among the cultivars tested, the Australian cultivars Kite and Hartog had among the lowest levels of seed set due to chilling and their responses were investigated further. The developmental stage at exposure, the chilling temperature and length of exposure all influenced the level of sterility. The early period of booting, and specifically the +4 cm auricle distance class, was the most sensitive and corresponded to meiosis within the anthers. The response of microtubules to chilling during meiosis in Hartog was monitored, but there was little difference between chilled and control plants. Other abnormalities, such as plasmolysis and cytomixis increased in frequency, were associated with death of developing pollen cells, and could contribute to loss of fertility. The potential for an above-zero chilling sensitivity in Australian spring wheat varieties could have implications for exploring the tolerance of wheat flower development to chilling and freezing conditions in the field.

Sustainable Management of Landfill Leachate by Irrigation

Leachate from domestic landfills is a significant environmentalhazard. In the urban environment, irrigation of recreational turf and parkland with nitrogen-rich landfill leachate providesboth low-cost treatment that minimises pollution of surroundingwaters and a valuable water resource. Of particular interest isthe capacity of the turf-soil system to ameliorate the ammonium-rich leachate. To address this issue, a two-year field trial was completed at the Newington Landfill irrigating with saline,ammonium-rich leachate. The field trial suggested that in situ bioremediation is sustainable provided that management strategies such as dilution of leachate to reduce solution electrical conductivity to 3.6 dS m-1 are adopted. Furthermore, pollution due to leaching of nitrogen can be minimised by managing the soil to enhance in situ denitrification of applied nitrogen. The management regimes adopted during the Newington field trial enabled nitrogen application rates in excess of 1400 kg NH4+ha-1 yr-1. However, the capacity of the system to ameliorate the leachate appears limited by soil salinity and sodicity rather than the control of nitrogen leaching by denitrification,suggesting that rates of up to 3500 kg NH4+ha-1 yr-1 may be viable if the salinity hazard can be effectively managed.

Cellular organisation and differentiation of organelles in pre-meiotic rice anthers

Pre‐meiotic cellular organisation of rice anthers has a great significance in pollen formation. We have used a combination of confocal laser and transmission electron microscopy (TEM) to characterise and differentiate organelles in pre‐meiotic rice anthers. Along with the characteristic organelles in the cytoplasm the epidermal cells of the pre‐meiotic rice anther are coated on their outer surface by a conspicuous bi‐lamellate cuticle. Chloroplasts of the endothecium contain immature grana, thylakoids and also starch granules. These plastids clearly contain photosynthetic pigments as shown by autofluorescence in confocal microscope studies. Both confocal and TEM studies reveal clusters of mitochondria in the middle layer. The tapetum contains electron opaque ribosomes, bundles of mitochondria and plastids. The nuclei of the tapetum occupy a large volume of the cytoplasm indicating the onset of mitotic prophase. Intense Rhodamine 123 staining reveals that a major portion of the structurally indistinguishable organelles that were seen throughout the densely ribosomic cytoplasm of sporogenous cells are mitochondria.

A modified ceramic sampler and lysimeter design for improved monitoring of soil leachates.

This paper describes the design and use of modified solution samplers and non-weighing lysimeters in a field experiment examining the response of a turf-soil system to landfill leachate irrigation over a 2-year period. The two designs were shown to offer significant performance advantages, were cost effective and overcame many of the reported problems commonly associated with each technique. The quantities of leached chloride detected in the 20%, 50% and undiluted leachate irrigated plots by the modified solution samplers (1,677, 4,319 and 8,021 kg ha(-1), respectively) and microlysimeters (1,759, 4,512 and 8,160 kg ha(-1), respectively) were significantly higher than the conventional sampler design (1,407, 3,767 and 7,052 kg ha(-1), respectively). Additionally, the microlysimeter design functioned reliably throughout the experiment, achieving solution flow rates analogous to the unconfined plots. Therefore, it was concluded that both the designs appear to be suitable for monitoring changes in soil solution composition associated with sub-surface wastewater irrigation.

The effect of sowing date, irrigation and cultivar on the growth and yield of wheat in the Namoi River Valley, New South Wales

SummaryA factorial experiment which examined the effects of sowing date, cultivar and irrigation frequency on the growth and grain yield of irrigated wheat was conducted at Narrabri, New South Wales. Irrigation scheduling was based on morning values of leaf water potentials (Ψl): plots were watered when Ψl, had fallen to either −0.8 MPa or −0.4 MPa or were not irrigated during the season.Maximum leaf areas, tiller numbers and total dry matter production were increased by more frequent irrigation, but subsequent tiller death and leaf senescence were generally not reduced by increasing watering. A delay in sowing from 23 June to 23 July reduced yields by 20%, on average. More frequent irrigation increased yields at both sowing dates, but a high protein, locally bred wheat (Songlen) responded less than a cultivar derived from the CIMMYT program (WW 15). The highest yield for Songlen was 570 g m−2 which was lower than the highest yield for WW 15 (730 g m−2); both were obtained from the −0.4 MPa treatment sown on 23 June. Compared with irrigated wheat grown in Mexico or southern New South Wales, dry matter production after anthesis at Narrabri was low. It was suggested that high temperatures after anthesis may limit post-anthesis productivity and subsequently, grain yields. The results of this experiment suggested that yields of irrigated wheat in the lower Namoi Valley can be improved through better irrigation management and varietal improvement, but the magnitude of this response may be limited by high spring temperatures.

Mechanism of low-temperature-induced pollen failure in rice.

Low‐temperature stress during microspore development alters cellular organization in rice anthers. The major cellular damage includes unusual starch accumulation in the plastids of the endothecium in postmeiotic anthers, abnormal vacuolation and hypertrophy of the tapetum, premature callose (1,3‐β‐glucan) breakdown and lack of normal pollen wall formation. These cellular lesions arise from damage to critical biochemical processes that include sugar metabolism in the anthers and its use by the microspores. Failure of utilization of the callose breakdown product and other microspore wall components like sporopollenin can also be considered as critical. In recent years, considerable progress has been made in the understanding of major biochemical processes including the expression of critical genes that are sensitive to low temperature in rice and cause male sterility. This paper combines a discussion of cellular organization and associated biochemical processes that are sensitive to low temperatures and provides an overview of the potential mechanisms of low‐temperature‐induced male sterility in rice.