Carbon Partitioning in Mature Leaves of Pepper: Effects of Daylength

Grange, R. 1. 1985. Carbon partitioning in mature leaves ofpepper: effects of daylength.—J. exp. Bot. 36: 1749–1759. The partitioning of recently fixed carbon has been examinedin mature pepper leaves grown in 6, 10 or 14 h photoperiodsat different irradiances chosen to give similar radiation integralsand in a 6 h photoperiod at the lowest of these irradiances.The partitioning of carbon into export, starch, sugars and respirationwas followed over the photopenod and the subsequent night ina mature leaf. The maximum export rate during the day (approximately 18 µgC cm^–2 leaf h^–1) was not significantly differentamong the treatments. Net photosynthesis rate was directly relatedto irradiance; the proportion of net photosynthesis exportedduring the day was 33% in 6-h days and 57% in 14-h days. Leafstarch accumulation (as a proportion of net photosynthesis rate)increased slightly when plants were grown in 6-h days. The remobilization of starch and sugars at night allowed exportrates to remain similar over 24 h when plants were grown in10-h or 14-h photoperiods. Leaves grown in 6-h days showed nosignificant changes in export rate during the first few hoursof night but exhausted their starch reserves during the nightand export rates declined. Sucrose and hexose levels decreased at the onset of darkness,but did not fall below 40 µg cm^–2 in plants grownin 10-h or 14-h photoperiods; when this level was reached after3–4 h of darkness, starch breakdown began. In leaves grownin both 6-h treatments, sucrose levels fell below 40 µgcm^–2 when starch reserves were depleted during the nightand the export rate decreased concurrently. The results are discussed in relation to the control of exportand starch metabolism in the leaf. Key words: Pepper, partitioning, daylength     

Embryo Water Status and Development of the Recalcitrant Species Quercus robur L: Determination of Water Relations Parameters by Pressure-Volume Analysis

The water status and water content of embryos of Quercus roburhave been determined during development. Using psychrometers,changes in osmotic potential at full imbibition and the proportionof water at zero reciprocal water potential, R₀, were estimatedfrom curves of embryo relative water content and reciprocalwater potential. The specific moisture content of embryos decreasedduring development, with a concomitant increase in the osmoticpotential. However, R₀ also increased such that, during thelast four weeks of development, there was little net changein the content of osmoticum per dry weight. Evidence is presentedthat starch stored in the cotyledon may be the major site ofmatrix-bound water, R₀. Isolated embryonic axes had a slightly higher osmotic potentialthan the whole embryo but the R₀ was much lower. The differencesbetween whole embryo and axis water relations parameters emphasizethe need to take account of R₀ when discussing seed water statusand survival. The results are considered in relation to currentmodels of seed water status and recalcitrant behaviour. Key words: Quercus robur L., embryo water relations, development, starch     

Characteristics of Starch Grains Isolated from Mature Pepper Leaves Grown under Different Irradiances and Daylengths

The size, shape and number of starch grains have been determinedin mature pepper leaves taken from plants grown under definedconditions of daylength and irradiance. Starch grains were 0.2–7.0 µm diameter and 02–1.5µm in thickness. Grain diameter was positively relatedto daylength and the number of grains per unit leaf area inverselyrelated to daylength. Mean grain diameter was also positivelyrelated to leaf area. Analysis of starch grains from leaves having a wide range ofstarch contents showed that grain diameter was linearly relatedto leaf starch content. However, mean diameter only doubledwith a 10-fold increase in starch content. The number of grainsincreased from approximately 5 ? 10¹⁰ m^–2 of leaf to over200 ? 10¹⁰ m^–2 with increasing starch content. The totalsurface area of grains increased from less than 1.0 m² m^–2leaf to over 20 m² m^–2 leaf. Leaf starch grain shape and size are compatible with both efficientstorage as disc-shaped chloroplasts and the maintenance of hightotal grain surface area by increasing grain number more thandiameter. Possible mechanisms for the control of grain initiation,growth and degradation are suggested. Key words: Starch grains, size, shape, pepper leaves     

Respiration and growth of tomato fruit

The respiration rate and diameter expansion growth of young tomato fruit were measured simultaneously and related to changes in carbon import and plant water status. Respiration rate was directly proportional to the volume expansion rate of fruit growing on isolated plant tops at a positive water potential, whether the growth rate was changed by changing the fruit temperature or by manipulating the source:sink ratio of the plants. From the latter relationship, the maintenance respiration rate was estimated by extrapolation to zero growth and was found to be about 25% of the respiration rate of the average fruit at 21°C. Alternatively, when carbon import was prevented by heat-ringing the fruit peduncle, the respiration rate of the fruit declined to about 40% of the control rate and remained steady, while the expansion rate then declined steadily to >10% of the control rate. These results show that fruit expansion was not contributing significantly to fruit respiration. Indeed, large fluctuations in fruit expansion rate could also be induced by repeated darkening and illumination of potted plants without a corresponding change in fruit respiration. Most significantly, fruit expansion was considerably reduced when plants were allowed to wilt, hut there was no change in fruit respiration rate unless the fruit peduncle was subsequently heat-ringed. We conclude that a major part of the respiration of young tomato fruit was determined by the rate of carbon import, or associated processes, and that fruit expansion per se can occur with relatively low respiratory costs.     

Carbon Partitioning and Export in Mature Leaves of Pepper (Capsicum annuum)

The partitioning of recently fixed carbon by mature pepper leaveshas been examined over a 10 h photoperiod using a constant specificradioactivity ¹⁴CO₂ labelling technique. Changes in the ratesof carbon partitioning into export, starch, sucrose and hexoseswere examined following changes in irradiance during the photoperiod.Leaves grown under 80 W m^–2 PAR were exposed to this irradiancefor the first 4 h of the photoperiod then the iiradiance wasdecreased. Leaves accumulated sufficient reserves in the first4 h to maintain export at the initial rate (approximately 20µg carbon cm^–2 leaf h^–1) over the following6 h of the photoperiod when the net photosynthesis rate (Pn)was decreased to 10% of the initial rate by the decreased irradiance.Export was initially maintained by the depletion of sucroseand hexose and then by carbon from the degradation of starchin the light. If leaves were exposed to low irradiance at the beginning ofthe photoperiod, then the export rate was linearly related tothe Pn during that period. When Pn exceeded that required tomaintain an export rate of approximately 20 µg carboncm^–2 h^–1, then more carbon was partitioned intostarch. At low initial irradiance, a greater proportion of photosynthatewas partitioned into export rather than starch and at high initialirradiancc the reverse occurred. There was a linear relationship between starch accumulationrate and Pn for all leaves but the relationship between Pn andexport rate was only significant for leaves with low levelsof reserve carbon. The results show that mature pepper leaves subjected to differentirradiances maintain constant export rates through alterationsof carbon partitioning. Export at low Pn is maintained at theexpense of sugar and starch reserves, with partitioning in highirradiance being predominantly to starch. Key words: Carbon partitioning, Starch, Export, Pepper (Capsicum annuum L.)     

Fluorigenic Glycosidase Substrates: Their Use in the Identification of some slow growing Mycobacteria

Glycosidase activity in slow growing mycobacteria was rapidly detected by the use of 4-methylumbelliferone-linked glycoside substrates. The species Mycobacterium nonchromogenicum, M. szulgai and M. marinum showed characteristic enzyme activities which distinguished them from the other species. M. marinum is unique among the mycobacteria so far examined in its possession of a very marked α-L-fucosidase activity. These fluorigenic glycosidase substrates should be of value in the identification of slow growing mycobacteria.     

The Extent of Starch Turnover in Mature Pepper Leaves in the Light

The extent of starch turnover in pepper leaves in the lighthas been estimated. After leaves were labelled with ¹⁴CO₂ atconstant specific activity for 4–7 h, the irradiance wasreduced to a level which caused no net change in the starchcontent of the leaf, and the supply of ¹⁴CO₂ was removed. Therewas no significant change in specific activity of starch overthe following 6–10 h, thus there was no exchange of ¹⁴C-starchwith ¹²C-assimilates entering the chloroplasts. Starch, turnover, ¹⁴C-labelling, pepper, Capsicum annuum L.     

Enzymic Breakdown of Amino Acids and Related Compounds by Suspensions of Washed Mycobacteria

The ability of washed mycobacteria, harvested from Lowestein-Jensen medium, to break down amino acids and related compounds was investigated. One hundred and thirty mycobacteria representing 17 species were tested against 21 compounds. Three compounds were broken down by all strains, seven were not attacked by any strain and in the remainder there was variable degradation both between and within species.     

Water relations and growth of tomato fruit pericarp tissue

The water relations of young tomato fruit pericarp tissue were examined and related to tissue expansion. The relationship between bulk turgor pressure and tissue expansion (as change in fresh mass or length of tissue) was determined in slices of pericarp cut from young, growing fruit by incubation in different osmotic concentrations of polyethylene glycol 6000 or mannitol. The bulk turgor of this tissue was low (about 0.2 MPa), even in fruit from plants that were otherwise fully turgid, whether measured psychrometrically or by length change in osmotic solutions. The rate of tissue growth at maximum turgor was less than that at moderate turgor unless calcium was added to the incubation medium. However, added calcium also decreased the rate of growth at lower turgor pressures. Yield turgor was < 0.1 MPa, but it was increased by the addition of calcium ions. Electrolyte leakage from tissue was greatest at maximum turgor pressure but was decreased by the addition of calcium ions or osmoticum. Tissue growth was unaffected by a range of plant growth regulators (IAA, abscisic acid, benzyladenine and GA₃) but was inhibited, particularly at high turgor, by low concentrations of malic or citric acid. The low turgor pressure of pericarp tissue could be due to the presence of apoplastic solutes within the pericarp, and evidence for this is discussed. Thus, fruit tissue may be able to maintain optimal expansion rates only at moderate turgor and low calcium concentration.     

An analysis of the accumulation of water and dry matter in tomato fruit

Abstract Previously published data from tomato plants grown in nutrient solutions having one of three electrical conductivities (2, 12 and 17 mS cm^?1) were analysed. The rate of water import into the fruit, and the proportion of this conducted by the xylem stream were calculated from the daily rates of transpiration and the net accumulation of water and calcium. The rate of water import decreased as the conductivity of the nutrient solution rose, the maximum daily import rates in the third week after pollination being 3.2, 3.0 and 1.8 g fruit^?1 d^?1 for fruit grown at 2, 12 and 17 mS cm^?1, respectively. During fruit development, the proportion of water imported via the xylem fell from 8–15% to 1–2% at maturity. The principal source of water for tomato fruit growth was phloem sap. Based on the daily rates of net dry matter accumulation, respiration and phloem water import, the calculated dry matter concentration of the phloem sap declined from 7 to 3%, or from 12.5 to 7.8% during fruit development in low or high salinity, respectively. The similar dry matter accumulation of fruit grown at different salinities was due to changes in both volume and concentration of phloem sap. Potassium salts in tomato fruit were calculated lo have contributed –0.29, –0.48 and –0.58 MPa to total fruit osmotic potential in the 2, 12 and 17 mS cm^?1 treatments, respectively, which accounted for 38% or 49% of the measured total osmotic potential of the 2 mS cm^?1 or 17 mS cm^?1 treatments. The contribution of hexoses to total fruit osmotic potential in the young fruit was from about –0.1 to –0.2 MPa at all salinities. The osmotic potential of tomato fruit is regulated more by potassium salts than by hexoses.