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This paper reports the ways that the differences in leaf senescence are related to grain filling, grain yield, and the dynamics of cytokinins (CKs) in the top three leaves of four field-grown new plant type (NPT) rice, a tropical japonica developed at the International Rice Research Institute, Philippines, to increase the yield potential of rice. The chlorophyll content in leaves decreased from flowering to maturity in all the NPT lines, whereas the grain filling percentage was higher in the fast-senescing NPT line than in slow-senescing NPT line. Grain yield was positively correlated with senescence in the flag leaf. Rapid changes in the CK levels were recorded in the leaves of the fast-senescing line, whereas the CK levels were relatively stable in leaves of the slow-senescing line, suggesting that the dynamics of CKs in the fast-senescing line are vital for fast senescence. There were no significant changes in bioactive CKs, CK O-glucosides (storage CKs), and cis-zeatin derivatives in different leaves of the slow-senescing NPT line between 0 and 3 weeks after flowering, suggesting that the content of these CKs is relatively stable during grain filling. A progressive increase in levels of bioactive CKs was positively correlated with gradual accumulation of CK N-glucosides (inactive CKs) in the top three leaves of the slow-senescing NPT line, whereas the decrease of bioactive CKs in the flag leaf of the fast-senescing line was accompanied by accumulation of CK O-glucosides. These results suggest that there is a higher rate of biosynthesis and/or import of bioactive CKs as well as their turnover which may favor delay of leaf senescence in the slow-senescing NPT line.

Changes in cellular calcium (Ca(2+)) handling are thought to underlie the altered contraction that occurs during cardiac hypertrophy and failure. Recent work has highlighted the importance of t-tubules in the control of intracellular Ca(2+). The present study was performed to investigate whether changes in the distribution of I (Ca) between the surface and t-tubule membranes might contribute to the altered Ca(2+) handling observed during compensated hypertrophy in the spontaneously hypertensive rat (SHR). Experiments were performed on ventricular myocytes isolated from 5-month-old SHR and normotensive Wistar-Kyoto (WKY) control rats. Osmotic shock using formamide was used to disrupt the t-tubular system and the whole-cell patch clamp technique used to monitor I (Ca) in the presence and absence of t-tubules. Membrane capacitance and I (Ca) were greater in control SHR than WKY myocytes; following detubulation, cell capacitance and I (Ca) both decreased and were no longer significantly different in the two cell types. The density of I (Ca) was not significantly different in control SHR and WKY cells or in detubulated myocytes from the two species. These data suggest that the distribution of I (Ca) is unchanged in SHR myocytes compared to WKY controls; I (Ca) density in the t-tubules was 1.2-fold greater than in the sarcolemma in both strains. These data also imply that the increase in surface area in SHR myocytes is due principally to an increase in t-tubular area, which is accompanied by an approximately equivalent increase in I (Ca), so that the density of I (Ca) at the cell surface and in the t-tubules remains the same. These changes would be expected to retain cell function and synchronicity of Ca(2+) release in the SHR at this stage of compensated hypertrophy.

The activities of transport mechanisms in epithelial cells are generally coordinated in order to minimise disturbances in cellular ion content and volume. Furosemide, a potent inhibitor of transport in the renal diluting segment, up-regulates apical K+ channel activity following the release of calcium from intracellular stores. The signal pathway between furosemide application and this calcium release is not known. Single early distal tubule segments from frog kidney were permeabilised with saponin in order to monitor calcium levels within cytoplasmic stores using the calcium-sensitive dye, mag-fura. The uptake (or release) of calcium to (or from) stores was initiated by adding agents to the bath solution, which is in direct contact with the intracellular organelles. ATP promoted calcium uptake into stores, whereas ATP removal led to a slower, spontaneous calcium release. Following loading, calcium stores could be rapidly depleted by inositol 1,4,5-trisphosphate (IP3), but not ryanodine. Calcium release was evident upon lowering the "intracellular" chloride concentration from 12 to 4 mM, equivalent to the fall in chloride induced by furosemide in intact cells. These results suggest that intracellular chloride may function as a second messenger, mediating cross-talk between the apical membrane and intracellular calcium stores.

The co-transformation of a single plant genome with two independent T-DNA regions provides opportunities for genetic separation in subsequent generations. In an effective strategy, co-delivery events must form a high proportion of the total transformed population. In this study, using the model plant species tobacco (Nicotiana tabacum), it was shown that the frequency of co-transformation within a given To population could be as high as 100% and this was found to be dependent, at least in part, on designing the plasmid vectors so that the kbp size of the first selected T-DNA region was >2-fold that of the designated T-DNA region for co-transfer. Overall, 40-50% of To lines demonstrated the capacity for segregational separation of co-transformed T-DNA regions. Hence, the estimate of the required number of total transformants for such an independent strategy may seem to be as little as 2-fold that for a conventional, single T-DNA strategy, but we strongly temper such estimates with indications that high co-transformation frequencies may be associated with a higher incidence of linkage. In this co-transformation study we used a single (Agrobacterium) strain system in which a single binary plasmid contained either two or three T-DNA regions, each with a selectable marker. This arrangement could reveal that 'read-through' events within the Agrobacterium cells, resulting in the co-transfer of adjacent T-DNA regions as a single linked unit, accounted for up to 20% of co-transformed plant lines. Such read-through co-delivery appeared to be more frequent from the 'supervirulent' EHA101 A. tumefaciens strain, compared to the 'ordinary' LBA4404 strain. By using the binary plasmid with three selectable T-DNA regions, we have been able to consider the frequency of co-integration of a third independent T-DNA within a T0 subpopulation of co-transformants. This was found to be higher than expected. These observations were applied to the co-transfer of (unwanted) plasmid backbone sequences and showed that screening against such sequences may add a significant factor in achieving the desired, final genotype.

Biological scientists are eagerly confronting the challenge of understanding the regulatory mechanisms that control the cell division cycle in eukaryotes. New information will have major implications for the treatment of growth-related diseases and cancer in animals. In plants, cell division has a key role in root and shoot growth as well as in the development of vegetative storage organs and reproductive tissues such as flowers and seeds. Many of the strategies for crop improvement, especially those aimed at increasing yield, involve the manipulation of cell division. This review describes, in some detail, the current status of our understanding of the regulation of cell division in eukaryotes and especially in plants. It also features an outline of some preliminary attempts to exploit transgenesis for manipulation of plant cell division.

Background An efficient method for the identification of medicinal plant products is now a priority as the global demand increases. This study aims to develop a DNA-based method for the identification and authentication of plant species that can be implemented in the industry to aid compliance with regulations, based upon the economically important Hypericum perforatum L. (St John’s Wort or Guan ye Lian Qiao). Methods The ITS regions of several Hypericum species were analysed to identify the most divergent regions and PCR primers were designed to anneal specifically to these regions in the different Hypericum species. Candidate primers were selected such that the amplicon produced by each species-specific reaction differed in size. The use of fluorescently labelled primers enabled these products to be resolved by capillary electrophoresis. Results Four closely related Hypericum species were detected simultaneously and independently in one reaction. Each species could be identified individually and in any combination. The introduction of three more closely related species to the test had no effect on the results. Highly processed commercial plant material was identified, despite the potential complications of DNA degradation in such samples. Conclusion This technique can detect the presence of an expected plant material and adulterant materials in one reaction. The method could be simply applied to other medicinal plants and their problem adulterants.