Louis J. Irving

Light-induced vegetative anthocyanin pigmentation in Petunia

The Lc petunia system, which displays enhanced, light-induced vegetative pigmentation, was used to investigate how high light affects anthocyanin biosynthesis, and to assess the effects of anthocyanin pigmentation upon photosynthesis. Lc petunia plants displayed intense purple anthocyanin pigmentation throughout the leaves and stems when grown under high-light conditions, yet remain acyanic when grown under shade conditions. The coloured phenotypes matched with an accumulation of anthocyanins and flavonols, as well as the activation of the early and late flavonoid biosynthetic genes required for flavonol and anthocyanin production. Pigmentation in Lc petunia only occurred under conditions which normally induce a modest amount of anthocyanin to accumulate in wild-type Mitchell petunia [Petunia axillaris×(Petunia axillaris×Petunia hybrida cv. ‘Rose of Heaven’)]. Anthocyanin pigmentation in Lc petunia leaves appears to screen underlying photosynthetic tissues, increasing light saturation and light compensation points, without reducing the maximal photosynthetic assimilation rate (Amax). In the Lc petunia system, where the bHLH factor Leaf colour is constitutively expressed, expression of the bHLH (Lc) and WD40 (An11) components of the anthocyanin regulatory system were not limited, suggesting that the high-light-induced anthocyanin pigmentation is regulated by endogenous MYB transcription factors.

The effects of salinity and osmotic stress on barley germination rate: sodium as an osmotic regulator

BACKGROUND AND AIMS Seed germination is negatively affected by salinity, which is thought to be due to both osmotic and ion-toxicity effects. We hypothesize that salt is absorbed by seeds, allowing them to generate additional osmotic potential, and to germinate in conditions under which they would otherwise not be able to germinate. METHODS Seeds of barley, Hordeum vulgare, were germinated in the presence of either pure water or one of five iso-osmotic solutions of polyethylene-glycol (PEG) or NaCl at 5, 12, 20 or 27 °C. Germination time courses were recorded and germination indices were calculated. Dry mass, water content and sodium concentration of germinating and non-germinating seeds in the NaCl treatments at 12 °C were measured. Fifty supplemental seeds were used to evaluate the changes in seed properties with time. KEY RESULTS Seeds incubated in saline conditions were able to germinate at lower osmotic potentials than those incubated in iso-osmotic PEG solutions and generally germinated faster. A positive correlation existed between external salinity and seed salt content in the saline-incubated seeds. Water content and sodium concentration increased with time for seeds incubated in NaCl. At higher temperatures, germination percentage and dry mass decreased whereas germination index and sodium concentration increased. CONCLUSIONS The results suggest that barley seeds can take up sodium, allowing them to generate additional osmotic potential, absorb more water and germinate more rapidly in environments of lower water potential. This may have ecological implications, allowing halophytic species and varieties to out-compete glycophytes in saline soils.

Protein Turnover in Grass Leaves

Abstract In this chapter, we discuss the processes of protein synthesis and degradation at the cellular, organ and whole-plant levels. In particular, we focus on the leaf protein Rubisco, which is important as both the most abundant form of N in most leaves and the carboxylating enzyme in photosynthesis. Chloroplasts contain the largest fraction of cellular N, divided approximately equally between soluble protein and thylakoid-associated N. Recently, small vesicles have been noted emanating from chloroplasts; however, there is considerable debate on the properties and regulation of these bodies. Similarly, recent investigations into the turnover of the D1 protein have questioned the orthodoxy view that D1 turnover is caused by oxidative fragmentation. The final two sections of this chapter look into the factors influencing the patterns of protein synthesis and degradation at the whole-leaf and whole-plant levels, and the implications that has for plant growth, development and productivity.

Morphology and Rubisco turnover characteristics of perennial ryegrass breeding populations after two and four cycles of divergent selection for long or short leaf length

Abstract. Perennial ryegrass populations previously subjected to two or four cycles of selection for short or long leaf length were studied to determine the response of morphological traits to selection and interaction to determine yield. Measured morphological traits were leaf length, leaf appearance interval, ligule appearance interval, leaf elongation duration, leaf elongation rate, tiller number, tiller dry weight, and herbage dry matter. Additionally, Rubisco concentration during leaf development was measured to determine the association of Rubisco turnover with morphological characteristics and yield. Rubisco was measured and modelled as a three-parameter (D, peak Rubisco concentration; G, time of D; and F, curve width measure), log-normal curve. Leaf length, leaf elongation rate, tiller weight, and plant dry matter diverged after two cycles of selection and further divergence occurred, with these traits being, respectively, 35, 28, 53, and 61% greater in the long- than the short-leaved plants after four cycles of selection. Opposite trends were displayed by Rubisco turnover, with selection for long leaves co-selecting for increased Rubisco turnover time and selection for short leaves resulting in increased leaf Rubisco concentration. There was indication of coupling of leaf appearance with Rubisco turnover. Across populations, multivariate analysis indicated that plant yield was associated with Rubisco concentration rather than Rubisco turnover. The association between higher yield and lower Rubisco concentration could be targeted in the breeding of high-yielding, nitrogen-efficient forage grasses. Plant yield was mainly associated with increased leaf area, indicating that yield could be improved by selecting for longer leaves and faster rates of leaf expansion.