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By pre-treatment of spinach chloroplasts with a high concentration of Tris buffer, 0.8 M, pH 8. 0, oxygen evolution coupled with DPIP or ferricyanide photoreduction was inactivated only when the chloroplasts were incubated in the light , but not in the dark. This inactivation of the chloroplast reaction was not due to chemical decomposition of Tris, but was probably due to the photoinhibition as reported by others. The photoinhibition was protected by the addition of DPIP in either oxidized or reduced form.It has been shown by many authors that oxygen evolution which is closely connected to the photosystem 2 of photosynthetic electron transport in higher plants is unstable than the photosystem 1 for various treatments, such as prolonged storage of chloroplastsl', heating, or treatments with detergents and lipase2-4'. Recently, Yamashita and Horio5' demonstrated that treatment of chloroplasts with high concentrations of Tris buffer resulted in the inhibition of the Hill reaction.We have studied the effect of Tris buffer in more detail in order to elucidate the oxygen evolving system of chloroplasts. On pre-incubating the chloroplasts in a high concentration of Tris buffer (0.8 M, pH 8.0) under weak light, oxygen evolution coupled with reduction of DPIP or f erricyanide (Hill oxidant) was inhibited, although no inhibition occurred in the dark. Material and MethodsChloroplasts were isolated from spinach leaves (Spinacia oleracea L.), using a conventional methods' and washed once with homogenizing medium (0.01 M KCI-0.05 M Tris-HC1 buffer, pH 7.5, containing 0.4 M sucrose). Washed chloroplasts were suspended in the same medium and each portion of the chloroplast suspension was treated with a high concentration of Tris buffer (0.8 M, pH 8.0) according to the following procedures. To 8 ml of 1.0 M Tris buffer, pH 8.0, 2 ml of the chloroplast suspension containing 0.5 mg chlorophyll per ml was added and mixed in an open Petri dish (8 cm in diameter). Final concentrations of Tris and chlorophyll in the mixture were 0.8 M and 0.1 mg per ml, respectively. Tris solution was freshly prepared before use. The mixture was then incubated for an appropriate time in the

OR. Five markers were significant (P < 0.05) for WEI; only one THRSP SNP remained significant following Bonferroni correction (Table 1).Comments: The current study emphasized genes with lipogenic activity and their relationship to reproductive events. Weaning-to-oestrus interval was associated with five SNPs. A single THRSP SNP maintained an association with WEI after correction testing. THRSP has been identified as a murine candidate gene within overlapping QTL for the effects of lifetime fertility and dietary restriction. 9 Data generated from this study imply that SNPs within lipogenic genes could be used to assist with identifying animals that tolerate the metabolic demands of lactation while maintaining reproductive competence.

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