Mitochondrial DNA in the T male-sterile cytoplasm (cms-T) of maize contains an open reading frame (ORF 13) associated with the T type of sterility. Antibodies raised to a chemically synthesized oligopeptide corresponding to ORF 13 were used to establish the expression of a 13-kDa protein from this reading frame. The 13-kDa polypeptide is synthesized uniquely in cms-T maize and purifies with the membrane fraction of T mitochondria. We assign the symbol urpf3-T to designate this mitochondrial gene. Presence of the nuclear restorer gene Rfl in cms-T plants results in a decrease in abundance of 13-kDa protein and alteration in the transcripts of urfl3-T.Cytoplasmic male sterility (cms) in higher plants represents one of the few well-characterized examples of heritable variability transmitted through the cytoplasm. Pollen production is aborted in cms plants, yet female fertility is unaffected. In maize (Zea mays L.), the trait has been used extensively in the commercial production of hybrid seed as a means of preventing self-fertilization. The three major malesterile cytoplasms of maize-S, C, and T-are distinguished according to the pattern of fertility restoration by nuclear restorer genes. The S and C cytoplasms require a single dominant restorer gene for fertility restoration-RJ3 and Rf4, respectively-whereas two restorer genes, Rfl and Rf2, are necessary to restore T cytoplasm cms (cms-T) plants to male fertility (1-4).In maize, abundant evidence indicates that changes in organization and expression of the mitochondrial genome are responsible for the cms trait (for review, see ref. 5). Maize plants carrying the T cytoplasm are also distinguished by an apparently inseparable association between male sterility and susceptibility to the fungal pathogen Bipolaris maydis, race T (6-8). This pathogen produces a host-specific toxin that affects the permeability of cms-T mitochondria and promotes the uncoupling of oxidative phosphorylation and the leakage of NAD+ and Ca2l (9-11). In contrast, mitochondria from male fertile (N), cms-C, and cms-S cytoplasms are insensitive to the toxin.Protein synthesis studies of isolated mitochondria have revealed differences between the protein products of T versus N mitochondria (12). In particular, a 13-kDa polypeptide is observed in T mitochondria that is absent in N, and a 21-kDa protein is synthesized in N mitochondria that is not detected in T. The 13-kDa protein is further characterized by a dramatically reduced abundance in cms-T plants that are restored to fertility by nuclear restorer genes Rfl and Rf2 (13).We have previously reported the identification of a highly rearranged DNA sequence, designated TURF 2H3, unique to the T cytoplasm of maize and associated with this type of sterility (14). TURF 2H3 contains two major open reading frames, ORF 13 and ORF 25, which may encode polypeptides of 13 and 25 kDa, respectively. The organization and transcription of ORF 13, so far as we know, are unique to the T cytoplasm of maize. Significantly, ORF 13 transcripts are modified...
The Texas male-sterile cytoplasm (cms-T) of maize carries the cytoplasmically inherited trait of male sterility. Mitochondria isolated from cms-T maize are specifically sensitive to a toxin (BmT-toxin) produced by the fungal pathogen Bipolaris maydis, race T, and the carbamate insecticide methomyl. A mitochondrial gene unique to cms-T maize, which produces a 13-kilodalton polypeptide associated with cytoplasmic male sterility, was expressed in Escherichia coli. After addition of BmT-toxin or methomyl, inhibition of whole cell respiration and swelling of spheroplasts were observed in Escherichia coli cultures producing the novel mitochondrial protein; these effects are similar to those observed with isolated cms-T mitochondria. The amino-terminal region of the 13-kilodalton polypeptide appears to be essential for proper interaction with the BmT-toxin and methomyl. These results implicate the 13-kilodalton polypeptide in conferring toxin sensitivity to mitochondria of cms-T maize.
A population of switchgrass, Panicum virgatum L., consisting of 33 half‐sib families was investigated over 2 years to obtain estimates of genetic parameters for several agronomic and nutritive traits, including height, maturity, dry weight, in vitro dry matter disappearance (IVDMD), and percent N. Dry weight was less heritable than other traits, with an individual narrow‐sense heritability of only 0.25. Narrow‐sense heritability for dry weight calculated on a family mean basis was 0.59. Dry weight and IVDMD were not significantly correlated while the correlation between dry weight and percent N was highly negative. Maturity was also negatively correlated with dry weight. The IVDMD and percent N, both measures of forage quality, had family narrow‐sense heritabilities averaged over three measurements per year of 0.79 and 0.74, respectively. Mean values for both traits were highest early in the season and declined markedly with maturity. The IVDMD and percent N were not significantly correlated. The estimated genetic parameters were used to form several selection indices involving three traits: dry weight, IVDMD, and percent N.
Subtropical perennial grasses make important contributions to productive, season-long grazing systems in the USA. The perennial bermudagrasses, particularly 'Coastal' bermudagrass (C}'nodon dac-t}'lon (L.) Pers.), are extremely productive, but high fiber allows only poor to moderate animal performance. Steer average daily gains (ADG) and productivity estimates of the subtropical perennials Oaccidgrass (Penni.retum flaccidum Griseb.), P. orientak Rich., and switchgrass (Panicum virgatum L.) were obtained. Sequential grazing of tall fescue (Festuca arundinacea Schreb.) and Coastal as a system (F + C) served as the standard for comparison. The grazing experiment with yearling steers was conducted on a Typic Hapludult soil for 3 years. Calendar days grazed, ADG (kg) and steers ha-1 , respectively, from initiation of grazing until Coastal was stocked (period 1) averaged 53, 0.93, and 15.1 for tall fescue; 20, 1.35 and 11.1 for Oaccidgrass and 40, 1.07, and 8.9 for switchgrass. Number of steers ha-1 was greatest on tall fescue and ADG lowest (P ::5 0.06). Flaccidgrass supported significantly more animals than switchgrass. Summer (period 2) results (avg. 98 days) for ADG and steers ha-1 , respectively, were 0.43 and 25.1 for Coastal; 0.78 and 9.1 for Oaccidgrass (P. orientak was similar), and 0.92 and 7.9 for switchgrass. Steer ADG was lowest and steers ha-1 highest on Coastal, while the other grasses were similar for both. Tall fescue made little contribution because rainfall was below normal all 3 years. Seasonal results from the F + C showed most calendar days (160), lowest ADG (0.59) but similar numbers of steers ha-1 (9.5) compared with respective values of 130, 0.90, and 9.6 for Oaccidgrass and 140, 0.96 and 8.2 for switchgrass. Flaccidgrass averaged significantly more steers ha -I than switchgrass. Gain ha -I from tall fescue in period 1 (792 kg) and Coastal in period 2 (1160 kg) was greater than the average for the other grasses, 349 and 559 kg, respectively. However, seasonal computations based on combined land areas for the F + C system yielded 1010 kg of gain ha-1 • That gain did not difl'er from the 930 kg ha-1 for the other grasses, even though the F + C system averaged 25 more calendar days. Flaccidgrass and switchgrass have quality attributes and a sufficiently long growing season to make an important contribution to an animal enterprise that values large daily animal responses. Coastal is more appropriately used in enterprises for an animal class, or portion of the season, where only moderate to low response animai-1 is required.AdditioiUil index words: Forage quality, Available forage, Stand persistence, Gain ha-1 , Total digestible nutrients ha-I, Panicum virgatum L., Penniaetum flaccidum Grise b., Penniaetum orientale Rich.
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