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Wheat is the world’s third largest food crop, and is relied upon as a food source by millions of people. Securing the supply of wheat is a problem because it is susceptible to many biotic and abiotic factors that limit production. One such factor, sprouting of the grain in the head, because of untimely rainfall prior to harvest, is a substantial problem worldwide. Pre-harvest sprouting has a significant impact on wheat growers, who suffer considerable economic hardship as a result of yield loss during harvesting and subsequent downgrading of their sprouted crops. Wheat processors are also affected by this problem, because sprouted grain has significantly altered chemical properties, making it unsuitable for its intended purpose, and often rendering it suitable for animal consumption only. This study investigated mechanisms of dormancy, in the diploid wheat Triticum tauschii (Coss.) Schmalh., to assess their suitability for use in hexaploid (bread) wheat to prevent pre-harvest sprouting. A soluble germination inhibitor was found in the bracts (palea, lemma and glumes) surrounding the grain of T. tauschii. Fractionation of an aqueous extract from the bracts, by HPLC, identified vanillic acid as being likely to be involved in this inhibition. Further analysis of the extract also identified a strong anti-oxidant capacity, indicating that part of the inhibition of germination may arise from the prevention of oxygen reaching the embryo.

Pre-harvest sprouting in wheat costs farmers millions of dollars every year. Pre-harvest sprouting tolerance (PST) has minimized this problem, but improvement of PST is still necessary. Synthetic hexaploid wheats (synthetics) have been used as sources of genes coding for many useful traits. Two studies evaluated the PST of a synthetic (Altar 84/Aegilops tauschii) and investigated its potential as a source of PST in crosses with wheat cultivars. The first study compared the synthetic with selected wheat checks for PST and with its parent Altar 84 for the germination response of these genotypes to controlled wetting treatments applied to field-grown intact spikes and threshed seed. Spikes were rolled in wet germination paper and the percentages of germinated seed were determined after seven days. Threshed seeds in Petri dishes were wetted with water and vegetative floral tissues (chaff) extracts. Germinating seeds were counted daily for 14 days. The synthetic was more tolerant than Altar 84 and was classified as moderately sensitive. The improved PST of the synthetic over Altar 84 was attributed to Aegilops tauschii. Seed dormancy and water-soluble substances in the chaff of the synthetic and other genotypes appeared to contribute to their PST. The second study used random inbred F��� lines obtained from single and backcrosses between the synthetic (red-seeded) and the sensitive wheat cultivars Opata F��� (red-seeded) and Bacanora 88 (white-seeded). Seed coat color and germination responses of the F5 lines subjected to a five-day spike wetting treatment were evaluated. Pre-harvest sprouting tolerance was moderately to highly inheritable and largely controlled by additive gene effects in the studied populations. An association between red seed coat color and PST was observed but white recombinant lines more tolerant than their sensitive parent were obtained. The synthetic can be used to improve wheats with red and white seed coats. The potential use of the synthetic as a PST source was discussed and a breeding strategy suggested. / Graduation date: 1999

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by Lee Yuen Chong. / Bibliography: leaves 112-131 / Thesis (M.Ph.)--Chinese University of Hong Kong, 1985

More than half of all spinal cord injuries are anatomically incomplete, yet many of these result in complete loss of motor function below the level of injury. One approach to enhance functional recovery is to exploit spared CNS axons (that extend past the point of injury) to sprout and connect to potential targets. We have previously found that application of the neurotrophin; BDNF, to the sensory-motor cortex stimulates expression of regeneration associated genes such as GAP-43, and Tαl tubulin, and results in enhanced sprouting of injured corticospinal fibers rostral to the site of injury. Here, we investigated whether infusion of BDNF into the intact sensorimotor cortex induces sprouting of undamaged corticospinal fibers into denervated cervical spinal cord. We also studied the effect of this treatment using several behavioral tasks: gait analysis, forelimb inhibition during swimming, and food pellet reaching task. The results show that BDNF infusion into the intact sensorimotor cortex subsequent to a unilateral pyramidal lesion increases (3.2 fold) the sprouting of intact corticospinal fibers into the denervated, contralateral grey matter at the lumbar level of the spinal cord when compared with vehicle treated rats. This effect was not seen at the cervical level of the spinal cord. Functionally, unilateral pyramidal injury of corticospinal axons significantly increased toe spread of the contralateral denervated forelimb and hindlimb when compared to the uninjured side. BDNF treatment showed a recovery to presurgical levels. Testing of fine motor control with a food pellet reaching task demonstrated deficits in the impaired forelimb but did not show any improvement due to BDNF treatment.

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