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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.

Sugar beet (Beta vulgaris) is an important arable crop, traditionally used for sugar extraction, but more recently, for biofuel production. A wide range of pests, including beet cyst nematode (Heterodera schachtii), root-knot nematodes (Meloidogyne spp.), green peach aphids (Myzus persicae) and beet root maggot (Tetanops myopaeformis), infest the roots or leaves of sugar beet, which leads to yield loss directly or through transmission of beet pathogens such as viruses. Conventional pest control approaches based on chemical application have led to high economic costs. Development of pest-resistant sugar beet varieties could play an important role towards sustainable crop production while minimising environmental impact. Intensive Beta germplasm screening has been fruitful, and genetic lines resistant to nematodes, aphids and root maggot have been identified and integrated into sugar beet breeding programmes. A small number of genes responding to pest attack have been cloned from sugar beet and wild Beta species. This trend will continue towards a detailed understanding of the molecular mechanism of insect-host plant interactions and host resistance. Molecular biotechnological techniques have shown promise in developing transgenic pest resistance varieties at an accelerated speed with high accuracy. The use of transgenic technology is discussed with regard to biodiversity and food safety.

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.

A strategy has been identified for the production of a low soil tare sugar beet by genetic manipulation of the table beet. This approach will involve increasing the sucrose storage capacity of the table beet by manipulating cell division in the cambial rings of the storage organ. Research aimed at the isolation of suitable cell division regulatory genes and storage organ specific promoter sequences is described. Sugar beet cdc 2 and cyclin sequences have been isolated by PCR techniques. Two root specific cDNA sequences have been characterized; one belongs to a group of hybrid proline-rich/hydrophobic proteins and the other resembles a gene induced during potato tuberisation.

The nuclear ribosomal internal transcribed spacer (ITS) sequences of eight Hypericum species were used to design H. perforatum-specific PCR primers by identification of short "microcode" sequences characteristic of the target species. These were tested with three vouchered H. perforatum DNA samples and eight samples from other species within the Hypericum genus. The most efficient primer combination, FO2 and HRI-S, amplified the genomic DNA from all three H. perforatum samples but not from any of the others apart from H. delphicum. The primer pairing was then tested against seven commercially available ornamental varieties of Hypericum; a positive result was obtained only with the H. perforatum sample. Three consumer products retailed as "St. John's wort" herbal remedies were sampled, two of which gave a positive result for H. perforatum. The assay was sensitive enough to detect 0.75 ng H. perforatum present as just 0.1 % of the total DNA. This method has the potential to be replicated in other plant species and presents a novel use for DNA barcoding data.

Cell growth and division are integrated with a programme of differentiation to determine the form of the plant body. In recent years the molecular controls of cell division and growth have been elucidated. Progression through the cell cycle is controlled by a family of serine/threonine protein kinases termed CDKs (cyclin-dependent kinases) that act in association with regulatory proteins termed cyclins. Specific CDKs associate with specific cyclins in order to bring about both the gene expression changes and the physical modifications that are necessary to complete the cell cycle. The nature and interactions of CDKs and cyclins have been studied in detail in mammalian and yeast cells but there is still relatively little information about such systems in plants. Much of the information is drawn by inference. Little is known about the coupling of cell division with cell growth and the integration of these processes into development.

A novel gene (RS2) has been isolated from a Beta vulgaris (cv. Regina) cDNA library. The expression of this gene was enhanced in the mature storage organ as compared to leaf tissue. The protein encoded by this gene was found to be alanine- and glutamic acid-rich and it resembles members of the latex allergen Hev b 5 family.

The sucrose storage capacity of the sugar beet, Beta vulgaris, storage organ has been related to its anatomy. A transverse section of the storage organ reveals a pattern of concentric rings which is caused by the alternation of vascular zones with parenchymatous zones. Sucrose is transported to the storage organ via the phloem and moves laterally to the adjacent parenchymatous tissues, where it is stored in the cell vacuoles. The storage organ of sugar beet has 12–15 cambia, the divisions of the 6 inner rings provide the cells which make up some 75% of the storage root while the outer rings (9 and above) make almost no contribution to the bulk of the storage root. It has been found that the small parenchymatous cells close to the phloem accumulate sucrose to a higher concentration than that achieved by large (older) cells remote from the phloem. Hence, it is predicted that for optimum sucrose accumulation the storage organ should have a large number of parenchymatous zones, each of which offers a short diffusion path from the phloem to predominately small storage cells. In order to manipulate sugar beet development toward this optimum it is necessary to have an understanding of the processes that regulate cell division, cell expansion and differentiation. Towards this end we have begun to isolate and characterise cell division cycle related genes from sugar beet and we have developed a cell suspension culture system for analysis of their roles (Elliott et al. 1996).