Comparative Growth of Excised Tomato Roots of Clones Carrying Dwarf and Normal Alleles

Abstract

ANALYSIS OF GENETICALLY kn own material by means of exci sed organ culture techniques should provid e information regarding genetic control of metabolism and growth of such mat erial. There are, for exa mple, a number of instances in which dwarfing is known to have a genetic basis. If roots excised fr om such plants were to sh ow the dwarf condition in culture, their growth und er controlled conditio ns, as compared with th ose showing the normal condition, could be subjected to va rious treatments designed to provide information which might be int erpreted in terms of the nature of genetic control. The purposes of this paper ar e to describe the establishment of several clon es of excised roots from such material which show the dwarf as well as normal condition in culture and to analyze some of the differences between them.MATERIALS AND METHODS.-Rick (1952) has reo ported a single gene mutation for dwarfness in tomat o. He calls this gene wd and describes the plant ca r ry ing it as a wilty dwarf which expresses its phenot ype only under field conditions. Th e gene d", an ext re me dwarf allele at the d locus , has been rep orted by Rick and Butler (1956) . Seed carrying the wd gene and the d" gene ind ependently, as well as compara ble lines carrying the normal alleles were kindly supplied by Dr. Charles M. Rick. Most of the observ ations reported in this paper have been made on the wd and iod" lines.Seeds were surface-sterilized in 1 per cent bromine wat er for ten minutes and allow ed to germinate under sterile conditions on moist filter paper in Petri di shes. When the primary roots were 30-SO mrn, long, 10 mm.-tips wer e excised aseptically and cultured according to standard techniques using White's medium (1943). Fresh weight of roots grown for a given period was obta ined as quickly as possible after pressing them once lightly between the pieces of filter paper. Dry weights were obtained after drying to constant weight in an oven at 105°C. In obtaining dry weights, 10 or more roots were used at each harvest. Nitrogen determinations were made by the micro-Kjeldahl method. Roots grown under standard conditions were killed and fixed in F.A.A. , cleared in 0.5 per cent sodium hydroxide, and length s of epidermal cells at different distances fr om the apex were determined usin g an eyepiece micrometer and a calibrated mechanical sta ge.RESULTS AND DISCUS SION.-Establishment of root clones.-wd and wd+ clone s.-At each planting 80 per cent or more of both wd and tod :" seed germi-lReceived for publication May 12, 1958. This work was supported in part by a gra nt from the University Re search Institute of The Univ ersity of Texas. Thanks ar e du e to Mr, Allan S churr for technical assistance. nat ed. The maximum number of uxl" seed germinated within 6 da ys, while it was 14 da ys before the ma ximum number of wd seed germinated. A few of the seedlings were transferred from the laboratory to the greenhouse, planted in soil and grown to maturity. The io d :" plants wer e extremely uniform but tho se of the usl lin...

STUNTED PLANT 1, A Gene Required for Expansion in Rapidly Elongating but Not in Dividing Cells and Mediating Root Growth Responses to Applied Cytokinin

“…For wild type, the increasing number of dividing cells in the zone of cell division increases the number of cells that flow into the elongation zone per unit time and hence increases the root's elongation rate. Although the growth of primary roots commonly accelerates with time after germination (Lee, 1958;Manos, 1961;Goeschl and Kays, 1975), the results here, to our knowledge, offer the first cellular explanation of the phenomenon. The stable number of dividing cells in stpl may reflect the number present at maturity in the embryo, or some limited increase may occur in the few days following germination (d 3-4 in the present protocol).…”

Variation in Excised Tomato Root Cultures

“…different sucrose concentrations optima) and thus not comparable for the determination of genetically controlled variation. Line 127 (the doubled haploid) and line 126 used in the present study had the same sucrose concentration optima although they differed in some other responses (Lee 1958b). The analysis of variance showed clearly that the two lines were significantly different, however, inter-clonal variations and test-to-test within clones were as obvious in the doubled haploid line (127) as in the mutated form from the same variety (126).…”

“…Comparative studies of excised roots among different species, varieties, and classes have revealed distinct differences in their growth rates, morphology, and metabolism (Street 1957;Boll 1954aBoll , 1954bLee 1954aLee , 1954bLee , 1958aLee , 1958b. Robbins (1941) alncd Whaley and Long (1944) have reported differences between the root cultures of two inbred tomato lines and their hybrid with the suggestion that heterosis had occurred.…”

Growth and Formation of Intercellularies in Root Meristenis

“…They are probably identical with the 'sinkers' described by Boll (1954 a, b), but since the identity is not clear, the provisory name of 'clwaris* will be used. They should not be confused with genetically sluw-gruwing roots of dwarf mutants iti tomato (Lee 1958).…”