Antifungal class I P-1,3-glucanases are believed to be part of the constitutive and induced defenses of plants against fungal infection. Unexpectedly, mutants deficient in these enzymes generated by antisense transformation showed markedly reduced lesion size, lesion number, and virus yield i n the local-lesion response of Havana 425 tobacco to tobacco mosaic virus (TMV) and of Nicotiane sylvestris to tobacco necrosis virus. These mutants also showed decreased severity of mosaic disease symptoms, delayed spread of symptoms, and reduced yield of virus i n the susceptible response of N.sylvestris to TMV, The symptoms of disease in the responses of both plant species were positively correlated with p-l,3-glucanase content i n a series of independent transformants. Taken together, these results provide direct evidence that ~-1,3-glucanases function in viral pathogenesis. Callose, a substrate for &l,&glucanase, acts as a physical barrier to the spread of virus. Callose deposition in and surrounding TMV-induced lesions was increased in the p-l,3-glucanase-deficient, local-lesion Havana 425 host, suggesting as a working hypothesis that decreased susceptibility to virus resulted from increased deposition of callose in response to infection. Our results suggest nove1 means, based on antisense transformation with host genes, for protecting plants against viral infection. These observations also raise the intriguing possibility that viruses can use a defense response of the host against fungal infection-production of ~1,3-glucanases-to promote their own replication and spread.

Antifungal class I [beta]-1,3-glucanases are believed to be part of the constitutive and induced defenses of plants against fungal infection. Unexpectedly, mutants deficient in these enzymes generated by antisense transformation showed markedly reduced lesion size, lesion number, and virus yield in the local-lesion response of Havana 425 tobacco to tobacco mosaic virus (TMV) and of Nicotiana sylvestris to tobacco necrosis virus. These mutants also showed decreased severity of mosaic disease symptoms, delayed spread of symptoms, and reduced yield of virus in the susceptible response of N. sylvestris to TMV. The symptoms of disease in the responses of both plant species were positively correlated with [beta]-1,3-glucanase content in a series of independent transformants. Taken together, these results provide direct evidence that [beta]-1,3-glucanases function in viral pathogenesis. Callose, a substrate for [beta]-1,3-glucanase, acts as a physical barrier to the spread of virus. Callose deposition in and surrounding TMV-induced lesions was increased in the [beta]-1,3-glucanase-deficient, local-lesion Havana 425 host, suggesting as a working hypothesis that decreased susceptibility to virus resulted from increased deposition of callose in response to infection. Our results suggest novel means, based on antisense transformation with host genes, for protecting plants against viral infection. These observations also raise the intriguing possibility that viruses can use a defense response of the host against fungal infection[mdash]production of [beta]-1,3-glucanases[mdash]to promote their own replication and spread.

Abstract. Quantification is a major problem when using histology to study the influence of ecological factors on tree structure. This paper presents a method to prepare and to analyse transverse sections of cambial zone and of conductive phloem in bark samples. The following paper (II) presents the automated measurement procedure. Part I here describes and discusses the preparation method, and the influence of tree age on the observed structure. Highly contrasted images of samples extracted at breast height during dormancy were analysed with an automatic image analyser. Between three young (38 years) and three old (147 years) trees, age-related differences were identified by size and shape parameters, at both cell and tissue levels. In the cambial zone, older trees had larger and more rectangular fusiform initials. In the phloem, sieve tubes were also larger, but their shape did not change and the area for sap conduction was similar in both categories. Nevertheless, alterations were limited, and demanded statistical analysis to be identified and ascertained. The physiological implications of the structural changes are discussed.

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Jaunin, F. and Hofer, R. M. 1988. Calcium and rhizodermal differentiation in primary maize roots.-J. exp. BoL 39: 587-593.Rhizodermal differentiation of maize (Zea mays L. cv. LG 11) roots cultured in humid air was influenced by a pretreatment for 2 h in CaCl 2 or CaSO* solutions. This increased the number of hair-producing roots and the density of hairs. Ethylene glycol-bis-{/?-aminoethyl ether)/VJV'-tetraacetic acid (EGTA) was inhibitory. Root hairs emerged in the part of the cell nearer to the tip. Trichoblasts were shorter and elongated more slowly than atrichoblasts. The elongation of the lower part of the trichoblast was less than that of the upper part.