The pressure microprobe was used to determine whether the turgor pressure in tomato (Lycopersicon esculentum Mill., variety "Castelmart") pericarp cells changed during fruit ripening. The turgor pressure of cells located 200 to 500 micrometers below the fruit epidermis was uniform within the same tissue (typically ± 0.02 megapascals), and the highest turgors observed (<0.2 megapascals) were much less than expected, based on tissue osmotic potential (-0.6 to -0.7 megapascals). These low turgor values may indicate the presence of apoplastic solutes. In both intact fruit and cultured discs of pericarp tissue, a small increase in turgor preceded the onset of ripening, and a decrease in turgor occurred during ripening. Differences in the turgor of individual intact fruit occurred 2 to 4 days before parallel differences in their ripening behavior were apparent, indicating that changes in turgor may reflect physiological changes at the cell level that precede expression of ripening at the tissue level.

Symptom development of Pierce's disease (PD) in grapevine (Vitis vinifera) depends largely on the ability of the bacterium Xylella fastidiosa to use cell wall-degrading enzymes (CWDEs) to break up intervessel pit membranes (PMs) and spread through the vessel system. In this study, an immunohistochemical technique was developed to analyze pectic and hemicellulosic polysaccharides of intervessel PMs. Our results indicate that PMs of grapevine genotypes with different PD resistance differed in the composition and structure of homogalacturonans (HGs) and xyloglucans (XyGs), the potential targets of the pathogen's CWDEs. The PMs of PD-resistant grapevine genotypes lacked fucosylated XyGs and weakly methylesterified HGs (ME-HGs), and contained a small amount of heavily ME-HGs. In contrast, PMs of PD-susceptible genotypes all had substantial amounts of fucosylated XyGs and weakly ME-HGs, but lacked heavily ME-HGs. The intervessel PM integrity and the pathogen's distribution in Xylella-infected grapevines also showed differences among the genotypes. In pathogeninoculated, PD-resistant genotypes PM integrity was well maintained and Xylella cells were only found close to the inoculation site. However, in inoculated PD-susceptible genotypes, PMs in the vessels associated with bacteria lost their integrity and the systemic presence of the X. fastidiosa pathogen was confirmed. Our analysis also provided a relatively clear understanding of the process by which intervessel PMs are degraded. All of these observations support the conclusion that weakly ME-HGs and fucosylated XyGs are substrates of the pathogen's CWDEs and their presence in or absence from PMs may contribute to grapevine's PD susceptibility.

SUMMARY Polygalacturonase-inhibiting proteins (PGIPs) are plant cell-wall proteins that specifically inhibit fungal endo-polygalacturonases (PGs) that contribute to the aggressive decomposition of susceptible plant tissues. The inhibition of fungal PGs by PGIPs suggests that PGIPs have a role in plant tolerance to fungal infections and this has been observed in transgenic plants expressing PGIPs. Xylella fastidiosa, the causal agent of Pierce's disease (PD) in grapevines, has genes that encode cell-wall-degrading enzymes, including a putative PG. Therefore, we hypothesized that PGIP expression could confer tolerance against this bacterium as well as against the fungal pathogen Botrytis cinerea. To test this hypothesis, Vitis vinifera cvs. 'Thompson Seedless' and 'Chardonnay' were transformed to express pear fruit PGIP-encoding gene (pPGIP) under the control of the CaMV 35S promoter. Substantial pear PGIP (pPGIP) activity was found in crude extracts from leaves and in xylem exudate of transgenic lines obtained from independent transformation events, but not in untransformed controls. pPGIP activity was detected in xylem exudate of untransformed scions grafted on to transgenic rootstocks expressing pPGIP. Leaves of transgenic plants infected with B. cinerea had reduced rates of lesion expansion. The development of PD was delayed in some transgenic lines with increased pPGIP activity. PD-tolerant transgenic lines had reduced leaf scorching, lower Xylella titres and better re-growth after pruning than the untransformed controls.

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The tolerance of crops to a shortage of boron (B) in the soil varies markedly among species. This variation in tolerance is due, in part, to a species ability to form phloem mobile B‐sugar‐alcohol complexes (such as B‐mannitol or B‐sorbitol) which enhance the remobilization of B within the plant. Species lacking the capacity to form B‐sugar alcohol complexes are intolerant of even short‐term deficits in soil B supply. Here we have genetically engineered rice (Oryza sativa L.) cultivar Taipei 309 (TP309) with the sorbitol‐6‐phosphate dehydrogenase (S6PDH) gene, a key enzyme for sorbitol production, and determined the effect of this transformation on the physiology of B remobilization. Sorbitol was detected in the S6PDH transgenic plants as well as in vector‐transformed plants and wild‐type (TP 309) plants, although the concentration of sorbitol in the S6PDH transgenic plants was significantly enhanced. Remobilization of B from mature leaves to flag leaves correlated with increased levels of sorbitol. The presence of sorbitol and detection of B remobilization in the wild‐type and vector‐transformed plants suggests that rice utilizes an unknown pathway for sorbitol synthesis and may partly explain the relative insensitivity of rice to B deficits when compared to other graminaceous crops.

Boron (B) remobilization, mannitol and glucose concentrations, and the effect of B application on changes in soluble carbohydrates were investigated in various organs of bearing `Manzanillo' olive trees (Olea europaea L. `Manzanillo'). Following foliar 10B application to leaves of various ages, there was significant 10B export out of the treated leaves, and significant 10B enrichment in nontreated adjacent organs, including inflorescences and fruit. Results demonstrated that B can be remobilized from leaves of various ages, and that foliar-applied B is phloem mobile in olive. Soluble carbohydrate analysis determined that mannitol and glucose are the predominant sugars in all organs analyzed and that the mannitol concentration in the leaves is adequate to account for all B transport. This is consistent with observations in other species, where the presence of mannitol is known to facilitate phloem B transport through formation of a mannitol-B complex. Previous reports have indicated that B application can alter carbohydrate metabolism. In the present study, foliar B application significantly suppressed glucose concentration in the leaf petioles of all ages and increased mannitol in petioles of the current-year-developed leaves.

An inbred line of chickens that develops severe scoliosis, an isogenic line and a line of birds derived from crossing the isogenic and inbred lines were used to study factors that influence the expression of scoliosis. Using the line of birds derived from the cross, the incidence of the lesion, defined as a spinal curve greater than 20 degrees, was influenced by deficiencies of copper, manganese or vitamin B-6. In the cross, scoliosis was expressed in 40-50% of birds. Vitamin B-6, manganese or copper deficiency, however, caused an increase in expression to 60-75% of birds. In contrast, protein deficiency, mild vitamin A deprivation, pantothenic deficiency, food restriction or calcium deficiency did not influence expression. Also, the addition of zinc (400 micrograms/g) or cadmium (5 micrograms/g) to a commercial nonpurified diet did not influence expression. That vitamin B-6, manganese and copper are dietary factors important to the expression of scoliosis may be related to their roles in the formation of connective tissue components, such as matrix glycoproteins, collagen or proteoglycans. For example, alterations and abnormalities in connective tissue may partly underlie progression of scoliosis and its potential for expression.

Higher plant inhibitors of fungal polygalacturonases are potential contributors to plant defense. To test this hypothesis we have raised antibodies against the `Bartlett' pear fruit polygalacturonase inhibitor (PGIP) and cloned a pear fruit PGIP cDNA. The pear PGIP cDNA was isolated by polymerase chain reactions based on our amino acid and nucleotide sequence information. Sequence analysis predicts a gene product of 34.5 kD with an isoelectric point of 6.02 in agreement with our biochemical data. Seven potential glycosylation sites are consistent with the glycoprotein character of these PGIPs. Southern blot analysis suggests the presence of 1 or 2 genes in the pear genome. Northern blot analysis indicates the presence of a transcript of 1.5 kb. Western blot analysis shows cross-reactivity of the anti-pear PGIP antibody to various dicot species as well as corn.