Paulo Roberto Mosquim

Respostas morfogênicas e estruturais de Panicum maximum cv. Mombaça sob diferentes níveis de adubação nitrogenada e alturas de corte

The morphogenetic and structural characteristics of Panicum maximum cv. Mombaca were evaluated in response to different levels of nitrogen supply and cutting regimes. The study was conducted in a glasshouse with natural conditions of light and temperature. Treatments corresponded to four levels of nitrogen supply (0, 50, 100 and 200 mg/dm3) and three cutting heights (5, 10 and 20 cm). The morphogenetic evaluations included leaf appearance and elongation rate, phyllochron and leaf lifespan. The structural measurements were: number of leaves, number of tillers and leaf lamina length of fully expanded leaves. The morphogenetic responses were affected by nitrogen supply during regrowth, highlighting the importance of that nutrient for manipulating sward structure. All variables responded positively to nitrogen supply, except phyllochron. Cutting height had a significant effect on leaf lifespan, leaf lamina length of fully expanded leaves and number of green leaves per tiller. Leaf appearance and elongation rate per tiller were increased in 133 and 104%, respectively, by nitrogen supply. The relationship between both group of variables was determinant for the characterization of the main vegetative changes on plants. The responses observed on morphogenetic characteristics comprise an efficient attribute to manipulate canopy structure, allowing improved allocation of productive resources to growth and developmental processes.

Leaf Gas Exchange and Chlorophyll Fluorescence Parameters in Phaseolus Vulgaris as Affected by Nitrogen and Phosphorus Deficiency

The effects of N and P deficiency, isolated or in combination, on leaf gas exchange and fast chlorophyll (Chl) fluorescence emission were studied in common bean cv. Negrito. 10-d-old plants grown in aerated nutrient solution were supplied with high N (HN, 7.5 mol m−3) or low N (LN, 0.5 mol m−3), and also with high P (HP, 0.5 mol m−3) or low P (LP, 0.005 mol m−3). Regardless of the external P supply, in LN plants the initial fluorescence (F0) increased 12 % in parallel to a quenching of about 14 % in maximum fluorescence (Fm). As a consequence, the variable to maximum fluorescence ratio (Fv/Fm) decreased by about 7 %, and the variable to initial fluorescence ratio (Fv/F0) was lowered by 25 % in relation to control plants. In LP plants, Fv/Fm remained unchanged whilst Fv/F0 decreased slightly as a result of 5 % decline in Fm. Under N deficiency, the net photosynthetic rate (PN) halved at 6 d after imposition of treatment and so remained afterwards. As compared to LN plants, PN declined in LP plants latter and to a less extent. From 12 d of P deprivation onwards. PN fell down progressively to display rates similar to those of LN plants only at the end of the experiment. The greater PN in LP plants was not reflected in larger biomass accumulation in relation to LN beans. In general, P and N limitation affected photosynthesis parameters and growth without showing any synergistic or additive effect between deficiency of both nutrients.

Photosynthesis in coffee (Coffea arabica and C. canephora) as affected by winter and summer conditions

Abstract Photosynthetic and biochemical responses of potted plants of Coffea arabica cv Red Catuai and C. canephora cv Kouillou were examined during winter and summer. There were large decreases in the photosynthetic rates of both cultivars from summer to winter, with more pronounced declines shown by Catuai. The photochemical efficiency of photosystem II, as evaluated by the ratio of variable to maximum chlorophyll fluorescence, decreased to a greater extent in Catuai than in Kouillou during winter. This probably was a secondary effect due to the loss of the photosynthetic capacity, which was mostly determined by non-stomatal factors. In response to winter conditions, Kouillou accumulated three times more proline and ascorbate with no changes in the content of malonedialdehyde (MDA). Catuai accumulated 160% more proline and 206% more MDA in winter in comparison to summer values, but there was no significant change in ascorbate levels. The content of chlorophylls and carotenoids did not change in response to natural seasonal acclimation. The leaf starch content in winter was higher by 53% in Catuai than in Kouillou. Photosynthetic rates, as measured by oxygen evolution, were well correlated with starch content in Catuai, but not in Kouillou. When winter-grown leaves were darkened for 96 h, their normal starch levels were halved; this was accompanied by the restoration of the photosynthetic rates to levels similar to those found in summer in both cultivars, with a concurrent resumption of the photosystem II efficiency.

Características morfogênicas e estruturais na rebrotação da Brachiaria brizantha cv. marandu submetida a três doses de nitrogênio

Um experimento foi disposto no delineamento em blocos casualizados, sob o esquema fatorial 3x8, tres dose de N (0, 20 e 40 mg dm-3 semana-1 de N) e oito tempos de rebrotacao (0, 2, 4, 8, 16, 24, 32 e 48 dias apos o corte de uniformizacao), em vasos, em casa-de-vegetacao, com tres repeticoes para cada tratamento, para avaliar as caracteristicas morfogenicas (taxa de aparecimento foliar [TApF] e taxa de alongamento foliar [TAlF]) e estruturais (comprimento medio de folhas [CMF], numero de folhas vivas perfilho-1 [NFVP], peso medio de perfilho [PMP] e densidade de perfilhos [DP]) da Brachiaria brizantha cv. Marandu. A TApF foi afetada significativamente com o aumento da dose de N. Plantas que receberam 40 mg dm-3 semana-1 de N apresentaram filocronos bem inferiores (6,99 dias folhas-1) aos encontrados na testemunha (12,20 dias folhas-1). A TAlF tambem foi bem sensivel a aplicacao de N, elevando-se significativamente com o aumento do suprimento de N, em torno de 185,24 e 264,32%, respectivamente, para as plantas que receberam 20 e 40 mg dm-3 semana-1 de N. O CMF sofreu efeito significativamente positivo com o aumento da dose de N. Tanto a dose de N quanto o tempo de rebrotacao tiveram efeito significativamente positivo sobre o NFVP e o PMP. Apesar do maior NFV, plantas que receberam doses de N tiveram maior perda por senescencia. Os fatores quantitativos estudados tambem tiveram efeito significativamente positivo sobre a DP.

TEOR E COMPOSIÇÃO DO ÓLEO ESSENCIAL DE CINCO ACESSOS DE MENTRASTO

This study aimed to analyse the content and the composition of the essential oil of five accesses of mentrasto (Ageratum conyzoides). Five accesses of mentrasto with three repetitions were used. The accesses were obtained in Mariana-MG (AMA), Piranga-MG (API), Visconde do Rio Branco (ARB) and Vicosa-MG (AVB and AVP). The essential oil was obtained by hydrodistillation and the identification of the oil components by CG and GC/MS. The ARB access presented the higher essential oil content, that is 0.70% (P < 0.05). Eleven chemical compounds were identified. The precocene I was the main constituent in the access API, and the precocene II was the main constituent in the accesses AMA, ARB, AVB and AVP.

Photosynthesis impairment in cassava leaves in response to nitrogen deficiency

Plants of cassava (Manihot esculenta Crantz cv. Cigana Preta) grown in a sand root medium were watered with nutrient solutions containing either 3 mM nitrate (low N) or 12 mM nitrate (high N). Chlorophyll concentration, chlorophyll a/b ratio, stomatal conductance, photorespiration rate and net carbon assimilation rate (on an area and a mass basis, but not on a chlorophyll basis) all decreased in low-N plants as compared with high-N ones. By contrast, photosynthetic nitrogen-use efficiency increased in low-N plants. As indicated by chlorophyll a fluorescence data, these plants exhibited increases in both excitation pressure on Photosystem II and thermal energy dissipation, with a corresponding decrease in quantum yield of electron transport, when contrasted with high-N plants. This decrease paralleled an unchanged maximal Photosystem II photochemical efficiency, suggesting a down-regulation of the Photosystem II photochemistry. It is proposed that decline in biochemical capacity for carboxylation, rather than stomatal limitation or electron transport, were the major constraints associated to the reduced photosynthetic rates induced by nitrogen deficiency in cassava plants.

Effects of nitrate nutrition on nitrogen metabolism in cassava

Two experiments were conducted independently with plants of cassava (Manihot esculenta Crantz) growing in sand with nutrient solutions with four nitrate concentrations (0.5, 3, 6 or 12 mM). In leaves, nitrate-N was undetectable at the low nitrate applications; total-N, ammonium-N, amino acid-N, reduced-N and insoluble-N all increased linearly, while soluble proteins did it curvilinearly, with increasing nitrate supply. In contrast, soluble-N did not respond to N treatments. Total-N and soluble proteins, but not nitrate-N or ammonium-N, were much higher in leaves than in roots. Plants grown under severe N deficiency accumulated ammonium-N and amino acid-N in their roots. Further, plants were exposed to either 3 or 12 mM nitrate-N, and leaf activities of key N-assimilating enzymes were evaluated. Activities of nitrate reductase, glutamine synthetase, glutamate synthase and glutamate dehydrogenase were considerably lower in low nitrate supply than in high one. Despite the low nitrate reductase activity, cassava leaves showed an ability to maintain a large proportion of N in soluble proteins.

ALUMINUM EFFECTS ON FATTY ACID COMPOSITION AND LIPID PEROXIDATION OF A PURIFIED PLASMA MEMBRANE FRACTION OF ROOT APICES OF TWO SORGHUM CULTIVARS

Aluminum (Al) effects on fatty acid composition and on the lipid peroxidation of a purified plasma membrane fraction of root apices of two sorghum cultivars were studied. Palmitic and linoleic acids were the major fatty acids in the root apices of sorghum, independent of the Al presence in nutrient solution. After Al treatment, the C18:0/C18:3 and C18:2/C18:3 ratios increased, while the C18:2/C16:0 ratio remained unchanged in the Al-sensitive cultivar but all three ratios decreased in the Al-tolerant cultivar. The double bond index and unsaturated fatty acid/saturated fatty acid ratio decreased in both cultivars but with higher intensity in the Al-sensitive cultivar. The linolenic and palmitic acids were probably the most important fatty acids associated with Al tolerance in the two sorghum cultivar studied. In the presence of Al, these two fatty acids decreased in the Al-sensitive cultivar but increased in the Al-tolerant cultivar. Plasma membranes obtained from the entire root system of the Al-sensitive cultivar showed higher concentration of malonaldehyde-thiobarbituric acid complex than the Al-tolerant cultivar, independent of the Al treatment. In root apices, in the absence of Al, there was no difference between cultivars. In the presence of Al, however, the concentration of the malonaldehyde-thiobarbituric acid complex increased about 43% but only in the Al-sensitive cultivar. So, under Al treatment, the Al-sensitive cultivar produced 36% more malonaldehyde-thiobarbituric acid complex than the Al-tolerant cultivar, which was taken as indicative of higher reactive oxygen species production and higher fatty acid peroxidation of the plasma membrane of this cultivar.

Carbon Partitioning and Assimilation as Affected by Nitrogen Deficiency in Cassava

Plants of cassava (Manihot esculenta Crantz) were raised in a sand root medium watered with nutrient solutions, under greenhouse conditions. As the N-supply increased, shoot dry mass was enhanced to a greater extent than root dry mass, thus leading to an increased shoot to root ratio. In leaves, contents of total soluble saccharides, non-reducing saccharides, and inorganic phosphate increased linearly with increasing N-supply. An opposite response was found for reducing saccharides and starch. In general, content of non-reducing saccharides was considerably greater than starch content. Activity of sucrose synthase was not detected, regardless of the N-treatments; by contrast, activity of neutral and acid invertases increased with increasing N-availability. Roots accumulated more total soluble saccharides, but less reducing saccharides and starch, as the N-supply increased. Photosynthetic rates decreased with increasing N-deficiency. Such a decrease was circumstantially associated to reducing saccharide, but not starch, accumulation. Results suggest a limited capacity for carbon export from source leaves under N-limitation.

Aspectos morfofisiológicos das cultivares de cafeeiro Catuaí-Vermelho e Conilon

n The objective of this work was to compare plants of the Coffea arabica†L. cv.†CatuaI- Vermelho and C.†canephora Pierre cv.†Conilon species in relation to the net photosynthesis rate and aspects of leaf anatomy. Coffea canephora plants presented higher net photosynthetic rate, transpiratory rate and leaf conductance rate than C.†arabica plants, which presented smaller photochemical capacity of photosystem†I, and shorter and thicker leaves than C.†canephora. Both species differed also in rela- tionship to the type, number and dimensions of stomata in the leaf epiderm: they are paracytics in C.†arabica and actinocytics in C.†canephora, and they are larger, but in smaller number in C.†arabica.