RESUMO
Delayed canopy senescence or 'stay-green' (SG) trait in maize (Zea mays L.) could improve drought tolerance. Two field trials comparing four to six maize hybrids with different senescence rate were carried out at Buenos Aires, Argentina, varying water availability during the reproductive period. Green leaf area at maturity was related to kernel weight (r2=0.94***) but its relationship with yield was weaker (r2=0.51-53*) and post-silking dry matter remobilisation was negatively related with the SG trait (r2=0.84**). Two additional experiments were carried out in 63 L pots by withholding irrigation in half of the pots after silking. The SG hybrid achieved lower root biomass at silking, a shallower root distribution and larger root growth in the post-silking period. Under drought conditions, stomatal conductance was lower in the SG hybrid but photosynthetic electron transport rate was higher. Higher post-silking dry matter assimilation in the SG hybrid was compensated for by higher dry matter remobilisation in the non-SG. Higher kernel number per plant in the non-SG hybrid with no ability to compensate for by higher kernel weight in the SG, resulted in slightly higher yields in the non-SG under drought. A water conservation strategy associated with a shallower root system could be linked to the SG trait, promoting faster water depletion at upper soil levels and reduced stomatal conductance at the leaf level but with no conclusive yield advantage.
Assuntos
Secas , Zea mays , Folhas de Planta , Solo , ÁguaRESUMO
While osteopenia (OPE) and osteoporosis (OPO) have been studied in various species of aging nonhuman primates and extensively in ovariectomized rhesus and cynomolgus macaques, there is virtually no information on the effects of castration on the skeleton of male nonhuman primates. Most information on castrated male primates comes from a few studies on the skeletons of eunuchs. This report used a subset of the Caribbean Primate Research Center's (CPRC) Cayo Santiago (CS) rhesus macaque skeletal collection to qualitatively and quantitatively compare the bone mineral density (BMD) of castrated and age-matched intact males and, thereby, determine the long-term effects of castration (orchidectomy) on bone. Lumbar vertebrae, femora, and crania were evaluated using dual-energy X-ray absorptiometry (DEXA or DXA) and digital radiography augmented, when fresh tissues were available, with autoradiography and histology. Results confirmed physical examinations of long bones that castration causes changes in the skeleton of male rhesus macaques similar to those found in eunuchs, including OPE and OPO of the vertebrae and femora, thinning of the skull, and vertebral fractures and kyphosis of the spine more severe than that caused by normal aging alone. Also like eunuchs, some castrated CS male rhesus monkeys had a longer life span than intact males or females. Based on these results and the effects of castration on other tissues and organs of eunuchs, on behavior, hormone profiles and possibly on cognition and visual perception of human and nonhuman primates, and other mammals, castrated male rhesus macaques should be used with caution for laboratory studies and should be considered a separate category from intact males. Despite these caveats, the castrated male rhesus macaque should make an excellent animal model in which to test hormone replacement therapies for boys and men orchidectomized for testicular and prostate cancer.
Assuntos
Densidade Óssea , Fêmur/fisiologia , Vértebras Lombares/fisiologia , Macaca mulatta/fisiologia , Orquiectomia/veterinária , Crânio/fisiologia , Absorciometria de Fóton/veterinária , Animais , Autorradiografia/veterinária , Masculino , Porto Rico , Intensificação de Imagem RadiográficaRESUMO
This cross-sectional study investigates the relationship between parity, bone mineral density, and spontaneous osteopenia/osteoporosis in a large skeletal population of female rhesus macaques (Macaca mulatta) from the free-ranging colony of Cayo Santiago, Puerto Rico. The sample consists of 119 mature female monkeys aged 4.0-22.2 years at time of death. The data consist of measurements of bone mineral content (BMC) and bone mineral density (BMD), obtained from dual-energy X-ray absorptiometry (DEXA) of the last lumbar vertebra. After controlling for age, there is a significant increase in BMD of the spine with increasing parity (P = 0.0006), up to a parity of 7 offspring. Thus, high parity initially has a positive effect on BMD in female rhesus monkeys, but this positive effect disappears with parities that are greater than 7 offspring. After controlling for parity, however, age has a negative (P = 0.015) effect on BMD, beginning several years after the attainment of peak BMD (age 9.5 years). Thus, it appears that parity initially mitigates the effects of aging, but the positive effect of parity on BMD is eventually overwhelmed by the aging process. Mean BMC and BMD values are higher in parous females compared to nulliparous females in the same age range. Similarly, females with low parity have significantly lower mean BMD values than do age-matched high-parity controls, and the frequency of osteopenia and osteoporosis is greater in low-parity females. Forty-three percent (43%) of the osteopenic/osteoporotic females in the sample are members of the low-parity group, even though it composes only 13% (16/119) of the entire sample. This study demonstrates that the free-ranging female rhesus monkeys from Cayo Santiago are a good nonhuman primate model for the study of bone mineral density, parity, osteopenia, and osteoporosis.