Lettuce (<i>Lactuca sativa</i>) is the most important crop in the group of leafy vegetables. It is characterized by considerable morphological and genetic variation. The crop comprises seven main groups of cultivars (including oilseed lettuce) differing phenotypically; they are usually described as morphotypes. Lettuce breeding is primarilly focused on various morphological features and resistance against diseases and pests. The accurate description of lettuce germplasm provides basic information useful for lettuce breeders. The construction of a lettuce descriptor list has been stimulated by the international genebank community. This list consists of 55 descriptors with 15 elucidated by figures. It provides a tool for detailed characterization of and discrimination within the intraspecific variation of <i>L. sativa</i>, verification of old varieties, and identification of putative duplicates and gaps in germplasm collections. These descriptors, along with descriptors of wild <i>Lactuca</i> species, provide an efficient analytical tool for studying the complex morphological variability of this genus and relationships among the species.
Cells of Bacillus megaterium 27 were challenged by a 30-min heat shock at 45 degrees C during various sporulation stages and then shifted back to a temperature permissive for sporulation (27 degrees C), at which they developed spores. Heat shock applied at 120 min after the end of the exponential phase induced synthesis of heat shock proteins (HSPs) in the sporangia and delayed the inactivation of spores at 85 degrees C. Several HSPs, mainly HSP 70, could be detected in the cytoplasm of these spores. An analogous HSP, the main HSP induced by increased temperature during growth, belongs to the GroEL group according to its N-terminal sequence. The identity of this protein was confirmed by Western blot (immunoblot) analysis with polyclonal antibodies against B. subtilis GroEL. Sporangia treated by heat shock immediately or 240 min after exponential phase also synthesized HSPs, but none of them could be detected in the spores in an appreciable amount. These spores showed only a slightly increased heat resistance.
Of about 100 Lactuca species, there are only 22 represented in world gene bank collections. The description of morphological and other important features of wild lettuce accessions and a correct taxonomic ranging increase their potential successful utilization. A broad study of 22 wild Lactuca species, their morphology, anatomy, karyology, DNA content and isozyme variation, and a search of large number of literature sources (description keys, floras, monographs) provided a base for an elaboration of a descriptor set. This set consists of 88 descriptors and 24 of them are elucidated by figures. It provides a tool for Lactuca species characterization and determination and for a discrimination of an infraspecific variation. Obtained data can be used for description of wild Lactuca genetic resources and also for research purposes.
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