Cladode Thickness Research Articles

Morphological and nutritional characterization of the cladodes of seven varieties of forage cactus of the genus Opuntia cultivated in Brazil

The plant species of the genus Opuntia are widely cultivated in the Semiarid region of Brazil and are considered as a sustainable technological alternative for coexistence with drought. The objective of this work was to characterize, by order of the cladodes, seven varieties of forage cactus of the genus Opuntia, cultivated under a rainfed regime, through morphological and nutritional parameters. The study was conducted at the IPA Experimental Station in the city of Caruaru-PE. The experimental design used was in randomized blocks, with three replicates. The varieties studied were: Gigante, Redonda, Clone IPA-20, F-08, Orelha de Elefante Mexicana, V-19 and Orelha de Elefante Africana. The number of total cladodes of the plant (NC), cladode length (CL), cladode width (CW), cladode area (CA), cladode thickness (CT), cladode volume (CV), cladode perimeter (CP), total fresh weight (FW), total dry weight (DW), total photosynthetic area (TPA), cladode area index (CAI), plant height (PH), plant width (PW), total fresh matter yield (TFMY), total dry matter yield (TDMY), total water accumulation (H2O), survival (SV), dry matter (DM), mineral matter (MM), organic matter (OM), neutral detergent fiber (NDF), acid detergent fiber (ADF), protein (P), hemicellulose (HEM), nitrogen (N), potassium (K) sodium (Na) and calcium (Ca) were determined at two years of age of the plants. Variability was observed in some of the morphological and/or nutritional characteristics among the order and/or phenological stage of the cladodes within the varieties. The varieties were divergent among themselves in the characteristics, NC, CL, CW, CA, CT, CV, CP, PH, PW, SV, P, N and Ca; and are related to genetic variation among the materials. The knowledge of the variability existing within and among botanical materials of forage cactus serves for the development of technologies aimed at each genetic material.

Effect of using hydrogel polymers on morphometric, forage production, and nutritional characteristics of cactus pear

The use of cactus pear has shown poor performance in some areas of semi-arid climate regions, as the species needs a wide gradient between temperatures during the day and night to develop, which does not occur in such zones. To lessen this negative occurrence, moisture availability provides better performance for the species, such as using hydrogel instead of irrigation. The objective of this study was to evaluate the effect of using hydrogel polymers on the production of cactus pear (Opuntia stricta cv. Mexican Elephant Ear). Three treatments with six replications were used, totalling 18 experimental units. The treatments were, (1) Conventional fertilization using fertilizer in granulated format; (2) Foliar fertilization with polymer using a dilution dose of 6 grams of polymer L-1 of water associated with the fertilizer in liquid form through the foliar route; (3) Foliar fertilization without polymer using only foliar fertilization in the same formulation as the treatment with polymer. There was no effect of fertilization strategy on plant height, cladode length, cladode width, cladode thickness, cladode area, and biomass. There was an effect of the fertilization strategy on dry matter, in which higher estimates were measured for conventional fertilization and foliar fertilization without polymer. On the other hand, foliar fertilization with polymer promoted increases of 13% in mineral matter and 42% in crude protein in relation to conventional fertilization. The fertilization strategy did not change the other chemical attributes of cactus pear. The use of the hydrogel did not influence the morphometric development of the Mexican Elephant Ear cultivar but promoted increments in the chemical composition.

Multivariate techniques for analyzing morphological characteristics of cactus pear genotypes in semiarid Brazil

The objective of this study was to identify variables with better discriminatory power between treatments and reduce the dimensions of the original data set. Multivariate principal component analysis (PCA) and dendrogram clustering techniques were used on a data set of morphological characteristics of cactus pear genotypes. The palm genotypes of the genera Nopalea and Opuntia were arranged in a completely randomized design, with 30 treatments and six replications. After 180 days of cultivation, morphological characteristics were evaluated, including plant height (PH) and width (PW), total number of plant cladodes (NCP), length (CL), width (CW), perimeter (CP), cladode thickness (CT), cladode area (CA), active photosynthetic area (APA) and cladode area index (CAI). Varimax rotation with Kaiser normalization was used to prevent variables with greater explanatory capacity from affecting the rotation. Measurements were obtained as part of cluster model generation, using a full set of morphological variables for subsequent analysis of principal component and cluster analyses. The main components obtained were efficient in reducing the total variation accumulated in 30 original variables correlated to two linear combinations, which explained 81.04% of the total variation present in the original variables. Grouping using the Ward hierarchical method formed 3 groups, namely, group I consisted of genotypes F27, F48, G1, G14, G15, G20, G3, PC2, PCD, PM, T72, V07 and V20; group II was composed of the genotypes BA, F16, F34, G4, G5, OEA, OEM, POEA, T35, T80 and V19 and; group III was composed of genotypes F24, PC1, PC3, PC4, PC5 and V17. PCA demonstrated that APA, CAI, CA, NCP, PH, PW and CT are morphological variables that determine the best palm characteristics. The association of cactus morphological variables varied according to the genotypes, within each genus Nopalea and Opuntia. The genotypes with the best morphological characteristics were F27, F48, G1, G14, G15, G20, G3, PC2, PCD, PM, T72, V07 and V20.

Calcium Oxalate and Other Cladode Features in <i>Opuntia ficus-indica</i> Resistant Cultivars to <i>Dactylopius coccus</i> Costa

Multipurpose cactus pear plant with great potential as a source of food and livestock faced a threat from Dactylopius spp in different countries. Specifically, D. coccus is an important pest damaging significant areas in Tigray-Ethiopia. Using pest-resistant cultivars is an important element of an integrated pest management strategy, and studying the mechanisms of resistance is vital. It can be chemical or physical such as oxalate crystals and other cladode characteristics. Cladode features of six cultivars (three O. ficus-indica, two O. cochenillifera, and one O. robusta) were examined for resistance to D. coccus in a completely randomized design (CRD) with three replications. ‘Rojo Pelón’ (O. ficus-indica), ‘Robusta’ (O. robusta), and ‘Bioplástico’ (O. cochenillifera) are resistant cultivars; and ‘Atlixco’ and ‘Chicomostoc’ (O. ficus-indica) and ‘Nopalea’ (O. cochenillifera) are susceptible. Cultivars showed a significant difference in cladode weight in g, and cladode length, cladode width, and cladode thickness in cm, where cladode thickness was higher in ‘Rojo Pelón’ followed by ‘Robusta’. Calcium oxalates number per mm was higher in ‘Bioplástico’ (20.7 ± 2.08) followed by ‘Robusta’ (18.9 ± 2.31) and ‘Rojo Pelón’ (15.9 ± 0.34); and similarly, epidermis thickness found higher in ‘Bioplástico’ (0.21 ± 0.032) and ‘Robusta’ (0.19 ± 0.014), but similar with ‘Rojo Pelón’ (0.18 ± 0.026). However, cuticle thickness didn’t show a difference among cultivars. Cladode thickness, calcium oxalate number, and epidermis thickness had positive correlations with resistance. These results demonstrate that calcium oxalate number and epidermis thickness might have a positive role in D. coccus resistance in O. ficus-indica. This feeding-barring role and the insect-plant interaction need to be studied.

Heterochromatin and polyploidy in Opuntia Mill. (Cactaceae: Opuntioideae): implications for plant breeding

ABSTRACT Despite the importance of polyploidy for the evolution of Opuntia, few researches have been focused to identify the ploidy of cultivars used in plant breeding programmes. We aimed to provide chromosome numbers, ploidy and heterochromatin band patterns of seven species and 24 cultivars from Opuntia, and investigate the relationship between phenotypic characteristics and ploidy in these species. All cultivars analyzed of Opuntia atropes, O. cochenillifera, and one cultivar of O. undulata are diploids, O. larreyi, one cultivar of O. stricta and two cultivars of O. undulata are tetraploids and all cultivars of O. ficus-indica, one cultivar of O. stricta and four cultivars of Opuntia sp. are octoploids. CMA/DAPI banding revealed the occurrence of terminal bands in all cultivars and pericentromeric bands in six cultivars. Polyploid species of Opuntia had superior mean values than diploid ones in relation to the cladode width, cladode length, cladode area, cladode thickness and plant height. Diploids had superior mean values than polyploids in relation to the number of cladodes. Polyploidy may be a useful tool for obtaining Opuntia cultivars with quantitative characteristics of interest.

Forage yield and structural responses of spineless cactus ‘Orelha de Elefante Mexicana’ at different planting densities

The objective was to evaluate the forage yield and structural responses of spineless cactus ‘Orelha de Elefante Mexicana’ (OEM) (Opuntia stricta (Haw.) Haw) at different planting densities. The experimental design was a randomized block with five treatments and four replicates, during two production cycles of 12 months each. The evaluated densities were 20,000; 25,000; 33,333; 50,000; and 100,000 plants ha-1. The increase in planting density caused a linear reduction in plant height, width, and mass, as well as in number of primary, secondary, tertiary, and overall cladodes. It also caused a linear increase in cladode area index, dry and green yield, water use efficiency, and forage accumulation rate. The increase in planting density promoted a quadratic effect on cladode thickness and dry matter content. Cladode thickness decreased with planting densities up to 47,500 plants ha-1 and increased from this point onwards. As for dry matter content, there was an increase up to the planting density of 61,428 plants ha-1 and a decrease from this point onwards. The increase in planting density of spineless cactus ‘Orelha de Elefante Mexicana’ caused changes in structural responses and in forage yield. The use of greater planting densities increased forage yield.

REUTILIZAÇÃO DA ÁGUA RESIDUÁRIA DA ORDENHA NA PALMA SOB DIFERENTES FREQUÊNCIAS DE IRRIGAÇÃO E ADUBAÇÃO

Objetivou–se avaliar o desempenho da palma miúda (Nopalea cochenillifera Salm Dyck), em cultivo adensado sob diferentes frequências de fertilização e irrigação com água de reuso no semiárido sergipano. O delineamento foi em parcelas subdivididas, com três repetições de quatro parcelas de irrigação (7, 14, 21 e 28) e um controle (sem irrigação) e quatro níveis de fertilização: adubação orgânica 1 (35t esterco bovino ha-1), adubação orgânica 2 (35t esterco ovino ha-1), química (150 kg de N ha-1) e fertirrigação (água residuária). Onde as variáveis de crescimento (Altura, TCV-Taxa de Crescimento Vertical; TCH-Taxa de Crescimento Horizontal; TApC-Taxa de Aparecimento de Cladódio) não demonstraram diferenças em relação a frequencia de irrigação com o controle; os NCT-Números de Cladódios Totais, o CC-Comprimento do Cladódio, EC- Espessura do Cladódio, VT- Volume Total e a EUA- Eficiência de Uso da Água, foram semelhantes entre os tratamentos e a LC-Largura do cladódio foi inversamente proporcional; frequências de irrigação de 7 e 14 dias foram semelhantes e maiores que 21 e 28 dias. No tratamento controle (sequeiro) obteve - se produtividade de 23,84 t MS ha-1, sendo a menor obtida quando comparada a maior produtividade da frequência de irrigação de 14 dias, que foi de 30,11 t MS ha-1. A frequência de irrigação de 7 dias promoveu melhores resultados morfológicos na palma. Podendo inferir que, aos 18 meses de idade, se o fator água não for limitante, a palma miúda pode atingir o ponto máximo de crescimento, sendo este, quando atingida a 5ª ordem de aparecimento de cladódios.

PLOT SIZE AND SHAPE FOR FIELD TRIALS WITH FORAGE CACTUS PEAR

This study aimed to determine the size and shape of experimental plots that provide maximum precision using relative information method. This trial was conducted at the Federal Institute of Bahia. Plant height, cladode length, cladode width, cladode thickness, cladode area, cladode area index, number of cladodes, cladode total area and yield were measured in the third production cycle, 930 days after planting. The plants, defined as basic units, were arranged in 39 plot sizes so that the crop would fill the whole experimental area. Then, plot shapes with higher relative information and equal plot size in basic units were selected. The experimental plot with eight basic units in size ensures higher efficiency in the experimental evaluation. This combination between size and shape, besides meeting all evaluation requirements of the characteristics normally assessed in studies with forage cactus pear, has the maximum control of soil heterogeneity, thereby decreasing experimental error and significantly increasing precision.

DEVELOPMENT OF FORAGE PEAR VARIETIES UNDER DIFFERENT WATER SALINITY LEVELS

This study aimed to evaluate the effect of different levels of water salinity in the development of two varieties of cactus pear (Opuntia and Nopalea). The spineless cactus is native from Mexico, but nowadays can be found in many places throughout the world. The experiment was performed at the Federal Institute of Ceará – IFCE/Campus Sobral. The experimental design was a randomized factorial 5 x 2, with five levels of salinity in the irrigation water (0.0; 5.0; 10; 15 and 20 dS m-1) and two varieties of cactus pear Small or sweet (Nopalea cochenillifera Salm-Dick) and ‘elephants ear’ (Opuntia sp) with four replications. Variables studied were: plant height (cm), length and circumference of the paddle (cm), cladode thickness (cm) fresh weight (g) and dry weight (g). The variety “elephants’ ear” is more suitable for cultivation under irrigation with saline water, because it presented a better vegetative performance compared to the small variety, being more tolerant to saline stress in different levels of salinity. The effect of the interaction between salinity and varieties showed a decrease for all variables analyzed, with reduction in forage development of palm varieties for higher salinity levels.

Forage yield, structural responses and chemical composition of spineless cactus Orelha de Elefante Mexicana in different water depths and irrigation frequencies

ABSTRACT: The objective was to evaluate the effects of water depths and irrigation frequencies on structural responses, forage yield and chemical composition of spineless cactus Orelha de Elefante Mexicana (OEM) (Opuntia stricta (Haw.) Haw), in adensed crop system. The experimental design was randomized blocks, in subdivided plots (3x4) with 4 replicates. The water depths were (100%, 75%, 50%, and 25% of ETc - crop evapotranspiration) and three water application frequencies (7; 14 and 28 days between irrigations). There was interaction for water use efficiency (WUE) and plant dry mass. Increasing water depths reduced WUE for all irrigation frequencies and plant dry mass was lower for 7 days compared to 14 and 28 days in 25% ETc. Greater water depths increased linearly the plant height and plant width. First and second order cladode length, second order cladode dry mass (kg), fresh mass yield (FMY) (kg ha-1) and dry mass yield (DMY) (kg ha-1) had a quadratic response with the increase in water depth. The FMY and DMY increased up to 77% and 75% ETc, respectively. Irrigation frequency (28 days) promoted greater first order cladode length and cladode dry mass compared to 7 days. Cladode thickness in plant and basal cladode thickness were greater for 7 days compared to 28 days and 14 and 28 days, respectively, without influence on FMY and DMY. Irrigation frequencies from 7 to 28 days promotes similar forage production and water depths up to 77% ETc favors the forage yield for spineless cactus Orelha de Elefante Mexicana receiving supplemental irrigation.

Regression models for productivity prediction in cactus pear cv. Gigante

ABSTRACT The understanding of plant behavior and its reflexes on yield is essential for rural planning; thus, the biomathematical models are promising in the yield prediction of cactus pear cv. Gigante. This study aimed to adjust, through simple and multiple regression analysis, models for predicting the yield of cactus pear cv. Gigante. The study, using homogeneous treatments, was developed at the Instituto Federal Baiano, Campus of Guanambi, Bahia, Brazil. Data were collected in an area consisting of 384 basic units (plants), in which the yield, defined as a dependent variable, and the predictor variables: plant height (PH), cladode length (CL), cladode width (CW), and cladode thickness (CT), number of cladodes (NC), cladode area (CA), and total cladode area (TCA) were evaluated. Simple linear regression models, multiple regression models only with simple effects for the explanatory variables, and the multiple regression models considering the simple and quadratic effects, and all its possible interactions were adjusted. From this last model, a reduced model was obtained by discarding the less relevant effects, using the Stepwise methodology. The use of the vegetative traits, TCA, NC, CA, CL, CT, and CW, through the adoption of multiple linear regression, quadratic interaction or just the variable TCA by the use of simple linear regression, allows the yield prediction of cactus pear, with adjusted R² of 0.82, 0.76, and 0.74, respectively.

STRUCTURAL CHARACTERISTICS AND YIELD OF 'GIGANTE' CACTUS PEAR IN AGROECOSYTEMS IN THE SEMI-ARID REGION OF BAHIA, BRAZIL

ABSTRACT The adaptation capacity of forage cactus (Opuntia ficus-indica Mill) plants to edaphoclimatic conditions and plant responses to changes in management systems contribute to increase the use of this species in agriculture and the exploration of its productive potential in semi-arid regions. The objective of this work was to evaluate the structural characteristics and cladode yield of forage cactus plants grown under different agroecosystems in the semi-arid region of Bahia, Brazil. Structural characteristics of plants and soils attributes were analyzed. The traditional information on the crop management and its correlations with cladode yield were used to identify the best yield indexes, considering the peculiarities of each agroecosystem. Plant height, cladode thickness, and number of cladodes of the forage cactus plants evaluated were less affected by the agroecosystem than by the production systems. Cladode width, length, and area were more affected by the agroecosystems. The forage cactus crop yields, expressed by the annual cladode fresh matter yield, were positively correlated with the plant structural characteristics: plant height and thickness, and cladode width and length. The cladode weight per plant and fresh matter yield per area were the yield components most affected by the management system adopted by traditional producers.

Comparison of Methods for Harvest Prediction in ‘Gigante’ Cactus Pear

Behavior analysis and plant expression are the answers the researcher needs to construct predictive models that minimize the effects of the uncertainties of field production. The objective of this study was to compare the simple and multiple linear regression methods and the artificial neural networks to allow the maximum security in the prediction of harvest in ‘Gigante’ cactus pear. The uniformity test was conducted at the Federal Institute of Bahia, Campus Guanambi, Bahia, Brazil, coordinates 14°13′30″ S, 42°46′53″ W and altitude of 525 m. At 930 days after planting, we evaluated 384 basic units, in which were measured the following variables: plant height (PH); cladode length (CL), width (CW) and thickness (CT); cladode number (CN); total cladode area (TCA); cladode area (CA) and cladode yield (Y). For the comparison between the artificial neural networks (ANN) and regression models (single and multiple-SLR and MLR), we considered the mean prediction error (MPE), the mean quadratic error (MQE), the mean square of deviation (MSD) and the coefficient of determination (R2).The values estimated by the ANN 7-5-1 showed the best proximity to the data obtained in field conditions, followed by ANN 6-2-1, MLR (TCA and CT), SLR (TCA) and SLR (CN). In this way, the ANN models with the topologies 7-2-1 and 6-2-1, MLR with the variables total cladode area and cladode thickness and SLR with the isolated descriptors total cladode area and cladode number, explain 85.1; 81.5; 76.3; 74.09 and 65.87%, respectively, of the yield variation. The ANNs were more efficient at predicting the yield of the ‘Gigante’ cactus pear when compared to the simple and multiple linear regression models.

Morphological characterization of cactus pear (Opuntia ficus-indica) accessions from Agadir, Morocco

The North Africa region falls under arid and semi-arid climate and it is considered as a hot spot for climate change. To face feed shortage, increase income of the rural poor and to mitigate the effect of climate change, around 1 million ha of cactus crop has been planted in Tunisia, Algeria and Morocco. Aware of the importance of germplasm, in-situ collections are being initiated in the region where promising accessions have been introduced from many countries. The objective of this contribution was to assess the genetic diversity of 20 cactus pear accessions from the in-situ collection located in the INRA Morocco research station of Agadir using morphological characterization based on FAO-Cactusnet descriptor. The data were subjected to Principal Component Analysis (PCA) and Agglomerative Hierarchical Clustering (AHC) using XLSTAT 2015 package. The results showed that the accessions can be discriminated by the morphological descriptors. Many of these morphological descriptors are significantly correlated as the number of cladodes and the number of fruits (r=0.73), the number of cladodes and the plant diameter (r=0.73), the length of the cladode and the plant height (r=0.7), the length of the spine and the number of areoles (r=0.67). The cladode shape and the number of spines and areoles are the recommended descriptors, and are capable to discriminate accessions with a suitable accuracy. Other descriptors do not seem to influence the morphological characterization as the cladode thickness, the number of spine, the plant height and the cladode shape index. Therefore, Principal Component Analysis (PCA) and Agglomerative Hierarchical Clustering (AHC) are good tools to segregate accessions using a reduced number of morphological descriptors. Another important finding is that the number of morphological descriptors may be reduced without potential risk of reducing the accuracy of the phenotypic characterization.

Prediction of ‘Gigante’ cactus pear yield by morphological characters and artificial neural networks

ABSTRACT Estimating cactus pear yield is important for the planning of small and medium rural producers, especially in environments with adverse climatic conditions, such as the Brazilian semi-arid region. The objective of this study was to evaluate the potential of artificial neural networks (ANN) for predicting yield of ‘Gigante’ cactus pear, and determine the most important morphological characters for this prediction. The experiment was conducted in the Instituto Federal Baiano, Guanambi campus, Bahia, Brazil, in 2009 to 2011. The area used is located at 14° 13’ 30” S and 42° 46’ 53” W, and its altitude is 525 m. Six vegetative agronomic characters were evaluated in 500 plants in the third production cycle. The data were subjected to ANN analysis using the R software. Ten network architectures were trained 100 times to select the one with the lowest mean square error for the validation data. The networks with five neurons in the middle layer presented the best results. Neural networks with coefficient of determination (R2) of 0.87 were adjusted for sample validation, assuring the generalization potential of the model. The morphological characters with the highest relative contribution to yield estimate were total cladode area, plant height, cladode thickness and cladode length, but all characters were important for predicting the cactus pear yield. Therefore, predicting the production of cactus pear with high precision using ANN and morphological characters is possible.

Morphological variation in <em>Opuntia jaliscana</em> (Cactaceae)

The aim of this study was to describe morphological variations of Opuntia jaliscana in 5 wild populations in the state of Jalisco (Mexico). Populations were selected along an environmental aridity gradient, and 61 vegetative and reproductive characters from 25 individuals were measured per population. Quantitative characters were analyzed independently by a one-way ANOVA test using the site as variation factor. Subsequently, a discriminant analysis was performed. The discriminant analysis results showed that the 46% of the total variation was explained by the first four discriminant functions. The analysis of overall membership between populations indicated that individuals were correctly classified in 87% of cases. Pearson linear correlation between the most significant variables and the aridity index, showed a positive relationship to cladode thickness and diameter of the trunk. The population from Tierra Blanca shows an outlier behavior because of variation in cladode thickness and fruit size, which might be related to plasticity of individuals to have a greater availability of water, while in Los Vallejo the separation might be due to selection by management and use. The remaining populations exhibited some morphological variability without separation.

Cladode growth dynamics in Opuntia ficus-indica under drought

Cactus pear (Opuntia ficus-indica L. Miller) is a CAM plant with an extraordinary capacity to store water in its succulent stems (cladodes). However, the daily variations of cladode thickness is unknown. Studying cladode thickness fluctuations may be useful for the early prediction of plant dehydration stress. The objective of this study was to determine if age, water availability and temperature influence diel cladode shrinkage and enlargement dynamics in cactus pear. The experiment was conducted in a greenhouse from April to July 2014, using cactus pear plants, equally split into irrigated and unirrigated treatments, and unrooted cladodes detached from mother plants. Soil moisture content (SMC), soil water depletion over 24-h, cladode relative water content (RWC), cladode thickness, stomatal conductance (gs), cladode growth rates (area increase) and nocturnal malic acid accumulation were monitored in plants of various ages. Cladode shrinkage and enlargement dynamics were assessed using stem gauges and expressed as absolute growth rate (AGRthickness, μmmin−1). In unirrigated pots, drought decreased SMC, RWC,cladode thickness, cladode growth rate and gs. Younger cladodes lost water later than older ones. Detached cladodes exhibited gs activity 3–4 months after detachment. Trends of AGRthickness showed that there was a progressive reduction of diel swelling and shrinkage fluctuations as cladodes aged. Such fluctuations were minimized under severe drought when 1-year-old cladodes reached 8mm thickness and a RWC of about 45%. A positive correlation was found between SMC and AGRthickness. Temperatures were also directly correlated with AGRthickness, although this relationship was gradually lost as SMC decreased. Overall, cactus pears were able to maintain some growth at very low hydration levels, and cladode growth was highly responsive to rehydration after long periods of drought.

Salt stress increases the expression of p5cs gene and induces proline accumulation in cactus pear

Proline (Pro) is one of the most accumulated osmolytes in salinity and water deficit conditions in plants. In the present study, we measured the Pro content, the activity and the expression level of delta 1-pyrroline-5-carboxylate synthetase (P5CS: γ-glutamyl kinase, EC 2.7.2.11 and glutamate-5-semialdehyde dehydrogenase, EC 1.2.1.41), a key regulatory enzyme involved in the biosynthesis of Pro, in cactus pear ( Opuntia streptacantha) subjected to 6, 9 and 11 days of salt stress. Treatment with NaCl of O. streptacantha young plants resulted in a decrease in the cladode thickness and root length, and in a significant and gradual accumulation of Pro in young cladodes, in a time- and concentration-dependent manner. P5CS activity, studied as γ-glutamyl kinase, was reduced at all times as a consequence of salt treatment, except at the sixth day at 75 and 150 mM of NaCl, where a slight increase was observed. We isolated an open reading frame (ORF) fragment of p5cs gene. The deduced amino acid sequence of the P5CS protein exhibited 90.4% of identity with the P5CS protein from Mesembryanthemum crystallinum. RT-PCR analysis revealed that the Osp5cs gene of O. streptacantha was induced by salt stress at 9 and 11 days of treatment. Furthermore, ABA-induced Osp5cs gene expression was observed in cladodes of cactus pear young plants. We observed an evident correlation between the transcript up-regulation and the Pro accumulation under salt stress; however, these results do not parallel with the changes in P5CS enzymatic activity. This Pro accumulation might function as an osmolyte for the intracellular osmotic adjustment and might be playing a critical role in protecting photosynthetic activity in O. streptacantha plants under salt stress.

Light-acclimation of cladode photosynthetic potentials in Casuarina glauca: trade-offs between physiological and structural investments.

Many arid and saline habitat species possess sparse canopies with cylindrical foliage that is considered relatively invariable along environmental gradients. However, even in sparse canopies strong gradients of light develop between the canopy top and bottom. We studied structural and photosynthetic acclimation to within-canopy light gradient in Casuarina glauca Sieb. ex Spreng., the photosynthetic organs of which are cylindrical cladodes. Seasonal average integrated quantum flux density (Qint) varied 25-fold between the canopy top and the canopy bottom. Cladode cross-sectional shape was unaffected by irradiance, but cladode dry mass per unit total area (MA) varied 2-fold within the canopy light gradient. This resulted primarily from light-dependent changes in cladode thickness (volume to total area ratio,V / AT) and to a lesser extent from changes in cladode density (D, MA = DV / AT). Nitrogen content, and the volume of mesophyll per unit surface area increased with increasing Qint and V / AT, resulting in positive scaling of foliage photosynthetic potential (capacity of photosynthetic electron transport and maximum Rubisco carboxylase activity per unit area) with light. However, nitrogen content per unit dry mass and the volume fraction of mesophyll decreased with increasing irradiance. This was explained by greater fractional investment in mechanical tissues in cladodes with greater volume to surface area ratio. This trade-off between photosynthetic and support investments reduced the cladode photosynthetic plasticity. Our study demonstrates a significant acclimation potential of species with cylindrical foliage that should be included in larger-scale carbon balance estimations of arid and saline communities.

Water Budgets and Root Hydraulic Conductivity of Opuntias Shifted to Low Temperatures

Cladodes (stem segments) of platyopuntias generally lose water as ambient temperatures decrease, even when the plants are in wet soil. Two weeks after shifting plants from day/night air temperatures of 30^⚬C/20^⚬C to 10^⚬C/1^⚬C, cladode thickness decreased 15% for Opuntia ficus-indica and 25% for Opuntia polyacantha. During this period, daily transpirational water loss gradually decreased, but root water uptake from the soil immediately decreased about 90%. As the temperature was decreased from 30^⚬C to 0^⚬C, the root hydraulic conductivity (L_p) for excised root segments also decreased about 90%, with larger fractional decreases occurring at lower temperatures. The large decrease in L_p at the lower temperatures was chiefly responsible for the accompanying cladode desiccation. Such net loss of cladode water is apparently essential for certain cacti to survive seasonally cold periods in the field.