Balancing photosynthetic light-harvesting and light-utilization capacities in potato leaf tissue during acclimation to different growth temperatures

We investigated the effect of temperature during growth and development on the relationship between light-harvesting capacity, indicated by chlorophyll concentration, and light-utilization potential, indicated by light- and bicarbonate-saturated photosynthetic oxygen evolution, in Solanum tuberosum L. cv. Norland. Conal plantles were transplanted and grown at 20°C for 2 weeks before transfer to 12, 16, 20, 24 and 28°C for 6 weeks. After 4 weeks of the temperature treatments, leaf tissue fresh weights per area were one-third higher in plants grown at 12°C vs those grown at 28°C. Conversely, chlorophyll content per area in tissue grown at 12°C was less than one-half of that of tissue grown at 28°C at 4 weeks. Photosynthetic capacity measured at a common temperature of 20°C and expressed on a chlorophyll basis was inversely proportional to growth temperature. Leaf tissue from plants grown at 12°C for 4 weeks had photosynthetic rates that were 3-fold higher on a chlorophyll basis than comparable tissue from plants grown at 28°C. These results suggest that the relationship between light-harvesting capacity and light-utilization potential varies 3-fold in response to the growth temperatures examined. The role of this response in avoidance of photoinhibition is discussed.     

Freezing tolerance, cold acclimation and oxidative stress in potato. Paraquat tolerance is related to acclimation but is a poor indicator of freezing tolerance

Potato is a species commonly cultivated in temperate areas where the growing season may be interrupted by frosts, resulting in loss of yield. Cultivated potato, Solanum tuberosum, is freezing sensitive, but it has several freezing-tolerant wild potato relatives, one of which is S. commersonii. Our study was aimed to resolve the relationship between enhanced freezing tolerance, acclimation capacity and capacity to tolerate active oxygen species. To be able to characterize freezing tolerant ideotypes, a potato population (S1), which segregates in freezing tolerance, acclimation capacity and capacity to tolerate superoxide radicals, was produced by selfing a somatic hybrid between a freezing-tolerant Solanum commersonii (LT₅₀=-4.6°C) and -sensitive S. tuberosum (LT₅₀=-3.0°C). The distribution of non-acclimated freezing tolerance (NA-freezing tolerance) of the S1 population varied between the parental lines and we were able to identify genotypes, having significantly high or low NA-freezing tolerance. When a population of 25 genotypes was tested both for NA-freezing and paraquat (PQ) tolerance, no correlation was found between these two traits (R = 0.02). However, the most NA-freezing tolerant genotypes were also among the most PQ tolerant plants. Simultaneously, one of the NA-freezing sensitive genotypes (2022) (LT₅₀=-3.0°C) was observed to be PQ tolerant. These conflicting results may reflect a significant, but not obligatory, role of superoxide scavenging mechanisms in the NA-freezing tolerance of S. commersonii. The freezing tolerance after cold acclimation (CA-freezing tolerance) and the acclimation capacity (AC) was measured after acclimation for 7 days at 4/2°C. Lack of correlation between NA-freezing tolerance and AC (R =-0.05) in the S1 population points to independent genetic control of NA-freezing tolerance and AC in Solanum sp. Increased freezing tolerance after cold acclimation was clearly related to PQ tolerance of all S1 genotypes, especially those having good acclimation capacity. The rapid loss of improved PQ tolerance under deacclimation conditions confirmed the close relationship between the process of cold acclimation and enhanced PQ tolerance. Here, we report an increased PQ tolerance in cold-acclimated plants compared to non-acclimated controls. However, we concluded that high PQ tolerance is not a good indicator of actual freezing tolerance and should not be used as a selectable marker for the identification of a freezing-tolerant genotype.     

Mitochondria contribute to increased photosynthetic capacity of leaves of winter rye (Secale cereale L.) following cold-hardening

Cold-hardening of winter rye (Secale cereale L. cv. Musketeer) increased dark respiration from ?2.2 to ?3.9 μmol O₂ m^?2s^?1 and doubled light-and CO₂-saturated photosynthesis at 20°C from 18.1 to 37.0μmol O₂ m^?2 s^?1 We added oligomycin at a concentration that specifically inhibits oxidative phosphorylation to see whether the observed increase in dark respiration reflected an increase in respiration in the light, and whether this contributed to the enhanced photosynthesis of cold-hardened leaves. Oligomycin inhibited light- and CO₂-saturated rates of photosynthesis in non-hardened and cold-hardened leaves by 14 and 25%, respectively, and decreased photochemical quenching of chlorophyll a fluorescence to a greater degree in cold-hardened than in non-hardened leaves. These data indicate an increase both in the rate of respiration in the light, and in the importance of respiration to photosynthesis following cold-hardening. Analysis of metabolite pools indicated that oligomycin inhibited photosynthesis by limiting regeneration of ribulose-1,5-bisphosphate. This limitation was particularly severe in cold-hardened leaves, and the resulting low 3-phospho-glycerate pools led to a feed-forward inhibition of sucrose-phosphate synthase activity. Thus, it does not appear that oxidative phosphorylation supports the increase in photo-synthetic O₂ evolution following cold-hardening by increasing the availability of cytosolic ATP. The data instead support the hypothesis that the mitochondria function in the light by using the reducing equivalents generated by non-cyclic photosynthetic electron transport.     

Hydroxamate-activated peroxidases in potato tuber callus. Interaction with the determination of the cytochrome and the alternative pathways

In potato (Solatium tuberosum L. cv. Bintje and Doré) callus a very active hydrox-amate-stimulated NADH-dependent O₂-uptake develops during the growth of the callus, which is caused by a peroxidase. More than 95% of the peroxidase activity is found in the 40000 g supernatant. The total activity may be as high as 1000 times the respiratory acitivity of the callus tissue. At least two fractions, obtained by Sephadex gel filtration, can be distinguished showing this peroxidase activity, one of about 15 kDa and one > 50 kDa. The main properties of both fractions are: a) Hydroxamate at 0.2–0.5 mM gives half-maximal stimulation. Maximal stimulation is observed with 1–3 mM benzhydroxamate (BHAM) and 1–15 mM salicylhydroxamate (SHAM). Higher concentrations, especially of BHAM, give less or no stimulation. b) Hydroxamates are not consumed during the reaction. c) Both NADH and NADPH can serve as the electron donor for the reaction. The affinity for NAD(P)H is very low (K_m near 10 mM). In the absence of hydroxamates NAD(P)H is only slowly oxidized, with an even lower affinity. d) The peroxidase can carry out two reactions: an O₂-consuming and a H₂O₂-consuming reaction. In both reactions one NAD(P)H is consumed. In the first reaction H₂O₂ is formed which can be consumed in the second reaction, resulting in an overall stoichiometry of 2 NADH consumed for each O₂ molecule and in the production of H₂O. e) The reaction is completely blocked by cyanide, superoxide dismutase (EC 1.15.1.1) and (excess) catalase (EC 1.11.1.6), but not by antimycin A or azide. This peroxidase-mediated O₂-uptake might interfere with respiratory measurements. In experiments with isolated mitochondria this interference can be prevented by the addition of catalase to the reaction mixture. The use of high concentrations of hydroxamate is not allowed because of inhibitory effects on the cytochrome pathway. In intact callus tissue hydroxamates only stimulate O₂-uptake in the presence of exogenous NADH. In vivo the peroxidase does not appear to function in O₂-uptake, probably because of its localization (at least partly in the cell wall) and/or its low affinity for NADH. The use of hydroxamates in the determination of cytochrome and alternative pathway activity is discussed.     

Changes in cytokinins during initiation and development of potato tubers

Cytokinin-like activity was assayed in stolons and tubers of Solanum tuberosum L. ssp. andigena (Juz. et Buk.) Hawkes cv. 165 grown in pots under controlled environment conditions. The plants were allowed to tuberise without the application of environmental or other external stimuli. The soluble sugar and starch contents of stolon tips and tubers were measured. Starch accumulation was a precise indicator of tuber initiation. Cytokinin-like activity began to increase in tubers with a diameter greater than 7.5 mm and, as assessed on a per tuber basis, was greatest in the largest size-category analysed. However, expressed as a function of fresh and dry weight, activity was greatest in tubers of 15–20 mm in diameter. Increases in cytokinin-like activity occurred subsequent to tuber formation, indicating that the tuberisation stimulus is unlikely to be cytokinin-like in nature.     

Synchronization of tuber formation in potato grown in vitro by cell division synchronization in axillary meristems of stem explants

Optimization of in vitro tuberization (formation and growth of stolons and microtubers) by synchronization of cell divisions in axillary meristems of initial stem explants induced by low nonfreezing temperatures was studied in potato (Solanum tuberosum L., cv. Lugovskoi) plants. The proportion of simultaneously dividing cells in axillary meristems of stem explants subjected to 2-h cold treatment at 4°C was in 2.6 times greater than in control material (without chilling). The analysis of growth of stolons and microtubers produced from the explants exposed to cold showed that synchronization of cell divisions in the meristems of initial explants resulted in synchronization of stolon and microtuber formation and production of microtubers of identical physiological age.     

Assessing the relationship between respiratory acclimation to the cold and photosystem II redox poise in Arabidopsis thaliana

We examined the effect of manipulating photosystem II (PSII) redox poise on respiratory flux in leaves of Arabidopsis thaliana. Measurements were made on wild-type (WT) plants and npq4 mutant plants deficient in non-photochemical quenching (NPQ). Two experiments were carried out. In the first experiment, WT and mutant warm-grown plants were exposed to three different irradiance regimes [75, 150 and 300 micromol photosynthetically active radiation (PAR)], and leaf dark respiration was measured in conjunction with PSII redox poise. In the second experiment, WT and mutant warm-grown plants were shifted to 5 degrees C and 75, 150 or 300 micromol PAR, and dark respiration was measured alongside PSII redox poise in cold-treated and cold-developed leaves. Despite significant differences in PSII redox poise between genotypes and irradiance treatments, neither genotype nor growth irradiance had any effect upon the rate of respiration in warm-grown, cold-treated or cold-developed leaves. We conclude that changes in PSII redox poise, at least within the range experienced here, have no direct impacts on rates of leaf dark respiration, and that the respiratory cold acclimation response is unrelated to changes in chloroplast redox poise.     

Water deficit enhancement of proline and α-amino nitrogen accumulation in potato plants and its association with susceptibility to drought

Potato plants ( Solanum tuberosum L. cvs 'Up-to-Date', 'Desiree', 'Alpha', 'Spunta', 'Elvira' and 'Troubadour') were exposed to cycles of water stress and relief during growth. Severe water deficit induced increased proline content 6- to 7-fold in nonturgid leaves which just started to wilt, and 8- to 27-fold in fully wilted leaves of potatoes. However, proline content was not affected during the early stages of stress development over a range of osmotic potentials in the leaves. The rising proline content was related to turgor loss of leaves independent of changes in the osmotic potentials, which indicates that proline involvement in osmoregulation of potato leaves is unlikely.
Repeated cycles of water stress and relief resulted in increased proline and α-amino nitrogen content in the tuber tissue of some of the cultivars. The smallest increase in proline content was obtained in 'Alpha' tubers and the content of α-amino nitrogen remained unaffected by the water stress. Concomitantly, 'Alpha' was the most drought-tolerant cultivar, as determined by its capacity to accumulate dry matter in tubers under stress conditions. On the other hand, in tubers of cultivars which were more susceptible to drought, a marked increase in proline and α-amino nitrogen was observed in response to water stress. The possible association of these findings with tolerance of potatoes to repeated short periods of drought is discussed.     

Characterization of potato genotypes by chlorophyll fluorescence during plant aging in a Mediterranean environment

Field experiments were conducted in Sicily (south Italy) during two seasons to characterize by chlorophyll (Chl) fluorescence four genotypes (Spunta, Sieglinde, Daytona, and Ninfa) of potato (Solanum tuberosum L.) for off-season production during plant aging and to analyse the possible relation between Chl parameters and tuber yield. Chl fluorescence parameters [initial fluorescence (F₀), maximum fluorescence (F_m), F_v/F_m, time in which maximal fluorescence occurs (T_max)] gained from Kautsky kinetics and Chl content were measured weekly, from 5^th to 6^th leaf appearance to beginning of plant senescence in the first season and to full plant senescence in the second season. F₀ and F_v/F_m were the most reliable Chl fluorescence parameters for the definition of genotypic differences while Chl content and T_max were the most reliable Chl parameters to predict plant aging. Tuber yield was highly correlated with Chl content, T_max, F₀, and F_m.     

The regulation of respiration and growth of potato tuber callus by endogenous ethylene. Suppression of ethylene action by 2,5-norbornadiene

The growth (fresh and dry weight increase) of potato tuber ( Solanum tuberosum L. cv. Bintje) callus discs was stimulated by incubation in air with 500 ppm 2,5-norbornadiene (NBD, a competitive inhibitor of ethylene action) and inhibited by incubation in air with 4 000 ppm NBD. Ethylene formation by the callus was stimulated by NBD. The development of the alternative pathway, measured in isolated mitochondria was inhibited by NBD in a concentration-dependent way. The alternative pathway capacity, measured in vivo, was inhibited by 4 000 ppm NBD, but not by 500 ppm. Uninhibited in vivo respiration, which consists of cytochrome path activity and alternative path activity, was stimulated by the treatment with 500 ppm NBD. The main contribution to this stimulation was made by the cytochrome pathway. In 4 000 ppm NBD-treated callus, uninhibited respiration seemed to be unaffected as a consequence of an inhibited cytochrome path activity, which was compensated by a stimulated alternative path activity. Both in 500 and 4 OIK) ppm NBD-treated callus the alternative path activity in vivo was stimulated.
The regulatory role for endogenous ethylene in potato tuber callus is discussed in relation to: 1) The induction of respiratory pathways, 2) the supply of reduction equivalents in vivo and 3) growth.     

Tuber on a chip: differential gene expression during potato tuber development

Potato tuber development has proven to be a valuable model system for studying underground sink organ formation. Research on this topic has led to the identification of many genes involved in this complex process and has aided in the unravelling of the mechanisms underlying starch synthesis. However, less attention has been paid to the biochemical pathways of other important metabolites or to the changing metabolic fluxes occurring during potato tuber development. In this paper, we describe the construction of a potato complementary DNA (cDNA) microarray specifically designed for genes involved in processes related to tuber development and tuber quality traits. We present expression profiles of 1315 cDNAs during tuber development where the predominant profiles were strong up- and down-regulation. Gene expression profiles showing transient increases or decreases were less abundantly represented and followed more moderate changes, mainly during tuber initiation. In addition to the confirmation of gene expression patterns during tuber development, many novel differentially expressed genes were identified and are considered as candidate genes for direct involvement in potato tuber development. A detailed analysis of starch metabolism genes provided a unique overview of expression changes during tuber development. Characteristic expression profiles were often clearly different between gene family members. A link between differential gene expression during tuber development and potato tissue specificity is described. This dataset provides a firm basis for the identification of key regulatory genes in a number of metabolic pathways that may provide researchers with new tools to achieve breeding goals for use in industrial applications.     

Growth,photosynthetic activity and tuber quality of two potato cultivars in controlled environment as affected by light source

In order to elucidate the effect of genetic material and light source and their interaction on plant performance of potato (Solanum tuberosum L.), we studied the influence of two light sources, white fluorescent tubes (WF) and red blue LEDs with ratio 8:1 (RB) and two cultivars, ‘Avanti’ and ‘Colomba’ grown in phytotron, on growth, leaf photosynthesis and photochemistry and tuber quality. Under WF, net photosynthesis (NP) increased from the vegetative phase until flowering, then decreased during tuber bulking, with no differences between the cultivars. Lighting with RB increased the NP and the PSII maximum quantum use efficiency compared to WF. RB reduced stem elongation in both cultivars, as well as the number and area of leaves, and the aerial biomass per plant in ‘Colomba’, compared to WF. Conversely, tuber yield was higher in plants under RB light in both ‘Avanti’ and ‘Colomba’. Light source did not influence the tuber content of starch and total glycoalkaloids, while it affected differently in the cultivars the protein content and the glycoalkaloid profile. Our results highlight how interactions between light source and genotype need to be considered for potato cultivation in controlled environment under artificial lighting.     

The dynamics of photosynthetic acclimation to changes in light quanlity and quality in three Australian rainforest tree species

Photosynthetic acclimation was studied in seedlings of three subtropical rainforest species representing early (Omalanthus populifolius), middle (Duboisia myoporoides) and late (Acmena ingens) successional stages in forest development. Changes in the photosynthetic characteristics of pre-existing leaves were observed following the transfer of plants between deep shade (1–5% of photosynthetically active radiation (PAR), selectively filtered to produce a red/far-red (R/FR) ratio of 0.1) and open glasshouse (60% PAR and a R/FR ratio of 1.1–1.2), and vice versa. The extent and rate of response of the photosynthetic characteristics of each species to changes in light environment were recorded in this simulation of gap formation and canopy closure/overtopping. The light regimes to which plants were exposed produced significant levels of acclimation in all the photosynthetic parameters examined. Following transfer from high to low light, the light-saturated rate of photosynthesis was maintained near pre-transfer levels for 7 days, after which it decreased to levels which closely approximated those in leaves which had developed in low light. The decrease in photosynthetic capacity was associated with lower apparent quantum yields and stomatal conductances. Dark respiration was the parameter most sensitive to changes in light environment, and responded significantly during the first 4–7 days after transfer. Acclimation of photosynthetic capacity to increases in irradiance was significant in two of the three species studied, but was clearly limited in comparison with that of new leaves produced in the high light conditions. This limitation was most pronounced in the early-successional-stage species, O. populifolius. It is likely that structural characteristics of the leaves, imposed at the time of leaf expansion, are largely responsible for the limitations in photosynthetic acclimation to increases in irradiance.     

Effect of formaldehyde and glutaraldehyde fixation on the immunochemical reactivity of potato virus A with monoclonal antibodies

Potato virus A (PVA) was treated with different glutaraldehyde concentrations at a range of different pH values, and its immunochemical reactivity and integrity was tested in various types of ELISA using a panel of six monoclonal antibodies. Glutaraldehyde fixation was compared with formaldehyde fixation, and there was no significant difference in reactivity between PVA non-treated and treated with formaldehyde, but almost the entire immunochemical activity was lost after treating with glutaraldehyde.     

甘蔗种质资源自然条件下耐寒性评价

为了解广西农业科学院甘蔗研究所种质资源圃(南宁)保存的400份甘蔗种质材料的耐寒性表现,在2008年初低温灾害的自然条件下,以蔗茎节间受害指数和节间生长点受害指数为基础,通过系统聚类方法将参试材料分为不同耐寒性表现类群。结果表明,2008年初的低温灾害属于阴雨霜冻类型,400份甘蔗种质材料可分为5个耐寒性表现类群,耐寒性强的材料有226份(56.50%),耐寒性较强的材料有103份(26.75%),耐寒性一般的材料有53份(13.25%),耐寒性较差的材料有7份(1.75%),耐寒性差的材料有7份(1.75%)。可构建甘蔗耐寒性指数(CTI):CTI=0.3×节间受害指数+0.7×节间生长点受害指数。节间生长点对低温伤害的敏感性高于蔗茎节间组织,建议作为耐寒性评价的重要指标之一;甘蔗耐寒性指数可以用于评价阴雨霜冻灾害下甘蔗种质材料的耐寒性。     

Use of a stress inducible promoter to drive ectopic AtCBF expression improves potato freezing tolerance while minimizing negative effects on tuber yield

Solanum tuberosum is a frost-sensitive species incapable of cold acclimation. A brief exposure to frost can significantly reduce its yields, while hard frosts can completely destroy entire crops. Thus, gains in freezing tolerance of even a few degrees would be of considerable benefit relative to frost damage. The S . tuberosum cv. Umatilla was transformed with three Arabidopsis CBF genes ( AtCBF1-3 ) driven by either a constitutive CaMV35S or a stress-inducible Arabidopsis rd29A promoter. AtCBF1 and AtCBF3 over-expression via the 35S promoter increased freezing tolerance about 2 °C, whereas AtCBF2 over-expression failed to increase freezing tolerance. Transgenic plants of AtCBF1 and AtCBF3 driven by the rd29A promoter reached the same level of freezing tolerance as the 35S versions within a few hours of exposure to low but non-freezing temperatures. Constitutive expression of AtCBF genes was associated with negative phenotypes, including smaller leaves, stunted plants, delayed flowering, and reduction or lack of tuber production. While imparting the same degree of freezing tolerance, control of AtCBF expression via the stress-inducible promoter ameliorated these negative phenotypic effects and restored tuber production to levels similar to wild-type plants. These results suggest that use of a stress-inducible promoter to direct CBF transgene expression can yield significant gains in freezing tolerance without negatively impacting agronomically important traits in potato.     

Effect of hypoxia on sugar accumulation, respiration, activities of amylase and starch phosphorylase, and induction of alternative oxidase and acid invertase during storage of potato tubers (Solanum tuberosum cv. Russet Burbank) at 1°C

The transfer of potato ( Solanum tuberosum ) tubers from 10 to 1°C was associated with an initial decline in the rate of CO₂ output followed by a rapid increase reaching, within some 12 days, a peak which was about 3‐fold higher than at 10°C. Thereafter the rate of CO₂ evolution declined gradually for the duration of the experiment. The specific rate of mitochondrial O₂ uptake decreased initially, followed by a rise to a level similar to that of mitochondria prepared from tubers stored at 10°C. Low temperature decreased by 30% the capacity of the cytochrome pathway while it sharply increased the capacity of the alternative pathway. Sucrose was the first sugar to accumulate at 1°C, followed after a delay of 6‐7 days by glucose and fructose. Low temperature induced within 4‐5 days a rise in amylase activity which increased by 10‐fold after 30 days. The increase was reflected in only two out of four existing isoforms. In addition a novel isoform of amylase was detected later in storage. The induction and the accumulation of invertase mRNA and extractable activity followed the increase in sucrose but preceded that of hexoses. The activity of starch phosphorylase isoforms was not affected by temperature. There was a 3‐fold increase in chlorogenic acid at 1°C. Hypoxia strongly inhibited the accumulation of sugars and chlorogenic acid, the increase in the amylase activity, and the appearance of the novel isoform. Low O₂ totally suppressed the induction of invertase mRNA and increased the capacity of the alternative oxidase. It did not, however, prevent the decrease in cytochrome capacity; neither did it affect the activity of starch phosphorylase isoforms.