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Item The effects of defoliation and shading in root growth of Lolium perenne L. : a thesis submitted for the degree of Doctor of Philosophy to Massey University(Massey University, 1971) Evans, P. S.The effects of defoliation, shading and dark on the growth and morphology of roots of Lolium perenne L. plants have been examined using glass fronted containers and a technique developed for measuring root lengths and numbers of apices. A single defoliation caused a rapid drop in root elongation followed by a more gradual recovery with the most severe defoliation treatment having the greatest effect. Repeated defoliation caused a prolonged depression of root elongation but some recovery occurred. The most severe treatment resulted in considerable root death. With shading, root elongation fell over the first 8 - 10 days and then recovered to near the control level. Both defoliation and shading caused an increase in the length per unit weight of the root systems. Root elongation of plants placed in the dark fell rapidly to near zero, the effect being comparable with that of defoliating plants to 2.5 cm or less. Defoliation of plants placed in the dark caused a more rapid fall in elongation. Supplying glucose or sucrose to the roots of plants defoliated to the extent that root elongation would otherwise have ceased maintained elongation at up to two-thirds of the level of undefoliated plants. Sucrose was marginally more effective than glucose with little difference between concentrations 1-6%. Benzyladenine and indole-acetic-acid marginally increased elongation in the presence of sucrose. Dark-treated plants responded in a similar manner to defoliated plants to sucrose. The level of soluble carbohydrates in the roots of plants defoliated or placed in the dark was seen to be low after root elongation ceased and recovered as root elongation recovered. However the level at the time most roots ceased elongating was higher than in other experiments where root elongation was near optimum. That under these conditions the addition of sucrose or glucose maintains elongation at up to two-thirds of the control level suggests that translocation of soluble carbohydrates to the root apex may be the limiting factor. This possibility is supported by the difference in levels of soluble carbohydrates in various parts of the plant following defoliation at two different times of the day. The technique used to measure soluble carbohydrates was not sensitive enough to permit analysis of the root tips and thus check the hypothesis. Apart from the requirement for soluble carbohydrates and the apparent associated translocation factor there is evidently some other factor (s) limiting root elongation of defoliated and dark-treated plants. The nature of this factor was not determined.Item Differential responses of tillers to floral induction in perennial ryegrass (Lolium perenne L.) : implications for perenniality : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Biology at Massey University, Palmerston North, New Zealand(Massey University, 2008) Williamson, Michelle LeighDevelopment of sustainable practices is an important goal in agriculture. One possibility involves the development of perennial cereal crops, but the mechanisms of perenniality first need to be understood. While in annual cereals flowering structures die following seed production, in perennial grasses, perenniality is achieved by maintaining at least one shoot in a vegetative state. There are two views on perennating tiller origin in perennial grasses: some authors suggest that all over-wintering tillers flower in spring and summer, leaving spring-initiated tillers to perennate, while others indicate that spring-initiated tillers are too immature to survive summer conditions, thereby implying that flowering must be prevented in some over-wintering tillers. An understanding of perenniality will therefore require an understanding of flowering control in these species. Temperate perennial grasses have dual induction requirements for flowering, where plants become competent to perceive inductive signals following vernalisation, and flowering is initiated by inductive photoperiods. Two hypotheses were formulated to test these models. The ‘environmental control hypothesis’ stated that all adequately vernalised perennial ryegrass tillers would flower on sufficient exposure to inductive photoperiods. Alternatively, the ‘spatial control hypothesis’ stated that in addition to the environmental mechanisms, a spatial control mechanism acts to regulate flowering. Two experiments were conducted to test these hypotheses. Perennial ryegrass and Italian (annual) ryegrass were induced to flower and differences between the annual and perennial habits at flowering time were observed. However neither hypothesis was proven. In the second experiment, flowering was studied in detail in individual tillers of perennial ryegrass. The eldest tiller flowered in all flowering plants. The second eldest tiller did not flower in 72% of plants with more than one reproductive tiller, while the third eldest tiller flowered in 94% of these plants. These data favour the spatial control hypothesis which suggests that a spatial regulatory mechanism might act to repress flowering in some competent perennial ryegrass tillers. These results were supported by studies of meristem morphology and by a preliminary gene expression study. Maintenance of older, established tillers in a vegetative state might allow the perennial plant a greater chance of survival during summer.