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Arabidopsis fbaliana leaves were examined in short-term (1 h) and long-term (1 O h) irradiance experiments involving growth, saturating and excess light. Changes in photosynthetic and chlorophyll fluorescence parameters and in populations of functional photosystem II (PSII) centers were independently measured. Xanthophyll pigments, 3-(3,4-dichlorophenyI)-l,l-dimethylurea (DCMU)-binding sites, the amounts of D1 protein, and the rates of D1 protein synthesis were determined. These comprehensive studies revealed that under growth or light-saturating conditions, photosynthetic parameters remained largely unaltered. Photoprotection occurred at light saturation indicated by a dark-reversible increase in nonphotochemical quenching accompanied by a 5-fold increase in antheraxanthin and zeaxanthin. No consistent change i n the concentrations of functional PSll centers, DCMU-binding sites, or D1 protein pool size occurred. D1 protein synthesis was rapid. In excess irradiance, quantum yield of O, evolution and the efficiency of PSll were reduced, associated with a 15-to 20-fold increase in antheraxanthin and zeaxanthin and a sustained increase i n nonphotochemical quenching. A decrease in functional PSll center concentration occurred, followed by a decline in the concentration of D1 protein; the latter, however, was not matched by a decrease in DCMU-binding sites. I n the most extreme treatments, DCMUbinding site concentration remained 2 times greater than the concentration of D1 protein recognized by antibodies. D 1 protein synthesis rates remained unaltered at excess irradiances.During the last decade studies of photosynthesis and photoinhibition in higher plants have been driven by many advances in our understanding and by the availability of new techniques for in vivo and in vitro investigations. Following the biochemical studies of Kyle et al. (1984) with photoheterotrophic Chlamydomonas, attention has focused on a central role for the synthesis and degradation of the D1 protein of the heterodimer of the PSII reaction center

Double degrees (also called joint or combined degrees) -programs of study combining two bachelor degrees -are increasingly popular in Australian universities, particularly among women. A case study using qualitative and quantitative surveys of current and past double degree students is presented. The study indicates that double degrees benefit students in providing a broad education and increasing skills and options. However, benefits are not fully realised because of administrative difficulties, lack of support and absence of 'learning communities'. These problems arise because double degrees sit outside the disciplinary structure of universities. As such, however, double degrees have potential to provide transdisciplinary education. We suggest initiatives that would improve the experience, performance and persistence of double degrees students. They would also build the skills of integration, boundary work, communication and teamwork associated with transdisciplinarity. These skills not only equip students for a range of employment; they are sorely needed in society. AbstractDouble degrees (also called joint or combined degrees) -programs of study combining two bachelor degrees -are increasingly popular in Australian universities, particularly among women. A case study using qualitative and quantitative surveys of current and past double degree students is presented. The study indicates that double degrees benefit students in providing a broad education and increasing skills and options. However, benefits are not fully realised because of administrative difficulties, lack of support and absence of 'learning communities'. These problems arise because double degrees sit outside the disciplinary structure of universities. As such, however, double degrees have potential to provide transdisciplinary education. We suggest initiatives that would improve the experience, performance and persistence of double degrees students. They would also build the skills of integration, boundary work, communication and teamwork associated with transdisciplinarity. These skills not only equip students for a range of employment; they are sorely needed in society.

Divergent theories on the mechanism behind, and the nature of, photoinhibition are discussed, especially in relation to observations made in higher plant leaves. Comparisons are made with ‘lower’ plant groups and results of in vivo and in vitro experiments are considered. Irradiance‐induced mechanisms involved in the regulation of PSII function and structure are discussed in connection with turnover of the DI protein. A model is presented in which a structural change in DI protein facilitates the formation of a population of dissipative PSII centres that do not participate in linear electron transport to PSI. We suggest a sophisticated regulatory mechanism whereby this variable PSII function is controlled with respect to both incident light and biochemical demand, a control which relies on feedback from both light and dark reactions.