The level of endogenous sugars was inversely related to nitrate availability in young cotton (Gossypiwm hksutwm L.) plants, with high nitrate causing a greater decline in sugar content of roots than of shoots. High nitrate (low sugar) plants also displayed relatively more shoot growth and less root growth than low nitrate (high sugar) plants. These data are consistent with the theory that roots are poor competitors for sugar, and that sugar supply is a major factor limiting root growth in nvo. (4,20). When available carbohydrate decreases (e.g. with low irradiance or low atmospheric CO2 levels) root growth is typically curtailed more than shoot growth. Conversely, when carbohydrate accumulates root growth increases more than shoot growth. It is evident that sugar supply is one of the most important factors limiting growth of the root system. The manner in which this sugar is partitioned among the various energy-requiring processes must therefore profoundly affect root functioning.Assimilation of N03 requires metabolic energy and C for amino acid skeletons, both of which are supplied by sugar in a heterotrophic organ such as a root. N03 is an important competitor for sugar in roots (4,20), and plants grown on high levels of NO3 display shoot to root ratios characteristic of low sugar plants (10,15,18,19). The effect of N03 on roots is particularly interesting and complex because it induces increased activity of NR2 (the first enzyme of the N03-assimilation pathway) at the same time that it depletes the roots' supply of sugar which supports N03 assimilation. In this report we consider the question of whether sugar level affects growth and N03 assimilation differently in roots of cotton plants. MATERIALS AND METHODS Plant Culture. Seeds of cotton (Gossypium hirsutum L. cv. Deltapine 16) were germinated in moist Vermiculite at 30 C and transferred after 3 days to buckets containing 16 liters of aerated nutrient solution. Each bucket contained six plants. The halfstrength Hoagland solution was modified to contain as the sole N source either KNO3 or urea at specified concentrations. The buckets containing the plants were placed in a growth chamber with a 14-hr daylength (240 ,uE m-2 sec' photosynthetically active quantum flux density) and maximum and minimum temperatures of 29 and 18 C, respectively. Plants were analyzed 2 weeks after transfer to the growth chamber. Nutrient solutions were not changed during the 2-week growth period. The solution pH was monitored but no adjustments were necessary.Girdling and Excision. After 2 weeks, plants grown on 1 mm NO3 were selected for uniformity and divided into three groups.Plants in the first group were detoppedjust below the cotyledonary node, and the roots were left in the nutrient solution. Plants in the second group were girdled with a jet of steam below the cotyledonary node. The steam caused extensive necrosis within a 1-cm length of stem, but no wilting, and microscopic examination showed no damage to xylem vessels. Plants in the third group were maintained a...
In vivo assay techniques for nitrate reductase activity were evaluated for their ability to predict nitrate assimilation rates of germinating dark‐grown cotton (Gossypium hirsutum L.) seedlings. Activity was measured with four in vivo assay techniques: either aerobic or anaerobic, and either with or without added nitrate in the assay medium. Assays without added nitrate in the medium allowed closer estimates of reduced N accumulation than did assays with added nitrate. Additionally, in the absence of added nitrate, the anaerobic assay provided a better estimate than the aerobic assay because of O2‐stimulated nitrite reduction. The results suggest that the in vivo assay for nitrate reductase best approximated nitrate assimilation rates with only endogenous nitrate as substrate.
The use of methyl bromide (MeBr) did not detract from the firmness or skin color of 'Delicious', 'Golden Delicious' or 'Granny Smith' apples. Fruit fumigation with MeBr rest&cd in a darkening of the objective and subjective internal flesh color of 'Delicious apples, particularly unwaxed apples treated with 48g MeBr/m3 at 20°C for 2 hr. Internal flesh color of 'Golden Delicious' apples was not influenced at 48g MeBr/m3 at 6°C for 2 hr. Fumigation with 32g MeBr/ m3 at 20°C or 56g MeBr/m3 at 6°C for 2 hr did not detract from the firmness or internal color quality of 'Delicious', 'Golden Delicious' or 'Granny Smith' apples after 60 days in storage. MeBr-treated apples displayed greater acidity and less ethylene production than control fruit. Higher MeBr treatment temperature and the use of wax on fruit directly influenced the reaction of apples to MeBr fumigation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.