Chlorophyll Ab Research Articles

PHYSIOLOGICAL RESPONSES OF SUNFLOWER TO WATER STRESS UNDER DIFFERENT LEVELS OF ZINC FERTILIZER

To investigate the physiological responses of sunflower (Helianthus annuus L., Alstar hybrid) to water stress under different levels of zinc fertilizer, an experiment was conducted at the Isfahan Agricultural Research Center, Isfahan, Iran, during 2008 and 2009 using a randomized complete block design within a split plot layout with three replications. Five irrigation treatments used in this experiment to impose water stress were IR1 (irrigation after 70 mm cumulative evaporation from class A evaporation pan (CE) during the entire growth cycle as control treatment), IR2 (irrigation after 120 mm CE during the entire growth cycle), IR3 (the same as IR1, except withholding one irrigation at initiation of peduncle elongating (R2)), IR4 (the same as IR1, except withholding one irrigation at the beginning of flowering (R5.1)) and IR5, (the same as IR1, except withholding one irrigation at 70 to 80% flowering (R5.7-8)). Irrigation treatments were allocated to main plots and three zinc fertilizer levels (0, 30 and 60 kg ha -1 of zinc sulfate) to subplots. Water stress reduced leaf relative water content (LRWC), chlorophyll a (CHLa) and b (CHLb), chlorophyll a/b (CHLa/b), total chlorophyll (CHLt), leaf area index (LAI), leaf dry weight (LDW) and head dry weight (HDW), but increased proline (PR) content of leaves. Sixty Kg ha -1 zinc sulfate fertilization could partly prevent deleterious effects of water stress at some occasions. This level of zinc sulfate application might be recommended under conditions similar to this experiment which sufficiency of soil zinc content to cope with water stress is in doubt.

Garlic physiological characteristics from harvest to sprouting in response to low temperature

Garlic is a perennial vegetable crop which belongs to liliaceae family and propagated by bulbs. Garlic sprouting depends on air temperature and its storage period. This study was conducted to investigate physiological trait variations from sprouting to harvest of garlic cv. White Gorgan stored in low temperature (4°C). Toward this end, variations of chlorophyll, carotenoid, carbohydrates, as well as the activity of Amylase and Invertase enzymes were measured before and after chilling treatment for 15 and 30 days. Obtained results showed a significant difference among measured traits (p < 0.01). Chlorophyll a, chlorophyll b, chlorophyll ab, carotenoid, glucose, and activity of Amylase and Invertase enzymes were increased in response to increment of chilling period which reached their highest values after 30 days. Sucrose and starch had the highest contents in the beginning of experiment and reached to their lowest value after chilling treatment (p < 0.01). Results of correlation analysis indicates negative correlation of all chlorophyll types with total sugar, sucrose and starch, while all chlorophyll types had positive correlation with glucose, a-amylase, b-amylase and Invertase. Increment of chilling treatment is followed by a-amylase and b-amylase increment as well as decreased starch content of Bulblets. Starch content showed a negative correlation with a-amylase and b-amylase. Also sucrose content was negatively correlated with invertase (p < 0.01). In conclusion, storage of garlic cv. White Gorgan in 4°C for 30 days had the best sprouting result. Key words: Garlic, sprouting, chilling, carbohydrate, enzyme.

Potential of Hyperion EO-1 hyperspectral data for wheat crop chlorophyll content estimation

Chlorophyll content is an essential biochemical parameter to track the main developmental stages and yield of cereals relevant for agriculture. In this perspective, several spectral chlorophyll indices have been developed to estimate chlorophyll content at both the leaf and canopy levels using remote sensing data and considering different crop types. The application of these chlorophyll indices under agricultural field conditions has not been rigorously tested and validated for wheat crops. The objective of this study is to investigate the relationship between a wide range of spectral chlorophyll indices and chlorophyll content of wheat crop using hyperspectral data acquired with the Hyperion Earth Observing 1 (EO-1) sensor and ground and laboratory measurements for validation purposes. The Hyperion data and ground measurements were acquired on 30 June 2002 over two agricultural fields near Indian Head, Saskatchewan, Canada. The image data were corrected for a spatial shift between the visible near-infrared (VNIR) and short-wave infrared (SWIR) detectors, destriped, and noise reduced. The data were then transformed to surface reflectance, corrected for sensor smile (1–3 nm shift in the VNIR and SWIR), and postprocessed to remove residual errors. The ground measurements included the leaf chlorophyll in arbitrary units using the soil-plant analyses development 502 (SPAD-502) meter and leaf chlorophyll content estimated from chemical laboratory analysis. The SPAD-502 measurements were correlated with laboratory-extracted leaf chlorophyll content to establish two calibration equations for the computation of chlorophyll ab (Chl ab) and chlorophyll a (Chl a) content, with a coefficient of determination (R2) of 0.72 and 0.69 and a root mean square error (RMSE) of 3.53 and 1.94 µg/cm2, respectively. The chlorophyll indices were derived from the Hyperion data and validated against those derived from a subset of the converted SPAD-502 measurements. The normalized difference pigment index (NDPI) showed the best results for wheat chlorophyll content estimation using the Hyperion data against those derived from the converted SPAD-502 measurements, with an index of agreement (D) of 0.66 and an RMSE of 2.89 µg/cm2. The performance of the NDPI at the wheat canopy level makes it a suitable tool to calibrate biophysical process models used in agriculture.

Changes in Freezing Tolerance, Water Potential, and Gene Expression of Poncirus trifoliata `Rubidoux' Seedlings Exposed to Acclimating Low Temperatures and Long Days

Poncirus trifoliata is a comparatively hardy, cross compatible, and graft compliant relative of Citrus. The citrus industry in Florida has suffered immense economic losses due to freezes. Although much research has been done in citrus freeze hardiness, little work has been on the early induction of freeze tolerance by low temperature. Poncirus trifoliata `Rubidoux' seedlings were germinated in perlite under intermittent mist at about 25°C and natural daylight conditions in a greenhouse and grown 2 weeks. See dlings were then transferred into a growth chamber at 25°C and 16 hour daylength for 1 week. Temperature was lowered to 10°C and tissue samples were collected at 0, 6, 24, and 168 hours. Freezing tolerance, at –6.7°C as determined by electrolyte leakage, and stem (leaves attached) water potential, measured using a pressure bomb, were also recorded for a subset of seedlings for the above intervals. After exposure to low temperature for 48 hours a red coloration became visible at the petiole leaflet junction an d at the buds, with subsequent exposure to low temperature the coloration spread to the leaves. Clones for phenylalanine ammonia lyase (PAL), 4-coumarate:CoA ligase (4CL), and chlorophyll ab binding protein (CAB), and chalcone synthase (CHS) were used to probe RNA isolated from P. trifoliata. PAL and 4CL transcripts increased in response to the low temperature. Significant increases in freeze hardiness occurred within 6 hours in the leaves, and increases continued for up to one week. Water potential increased from –0.6 to –2.0 MPa after 6 hours, then returned to –0.6 MPa after 1 week. These data indicate that increases in freezing tolerance and changes in water potential and gene expression can be detected shortly after low temperature treatments are imposed on P. trifoliata seedlings.

Isolation of a gene from maize encoding a chlorophyll a/b-binding protein

The chlorophyll a/b (CAB) proteins are major components of the light-harvesting complex of photosystems I and II in the thylakoid membranes of chloroplasts. The complexity of these peptides and the structure and relationship of distinct genes encoding them has been studied in detail in tomato, soya bean and Petunia [ 1, 2, 3 ]. This has led to the description of at least 5 classes of CAB genes in tomato based on differences between peptides found within and between PSI and PSII [ 8 ]. The different classes of CAB genes can be subdivided using another criterion, namely the presence of introns: type I genes do not contain introns whereas type I1 genes contain an intron in their coding sequence. One of the major features of CAB genes is their transcriptional regulation by light [ 10]. This leads to a major induction of CAB mRNA in lightgrown green tissues. In maize a CAB gene has been isolated which may represent up to 2~o of the mRNA in light-grown leaves [9]. However, this gene is also expressed to high levels in the dark. Here we describe the isolation of a structurally distinct maize gene encoding CAB. We have constructed a partial Sau3A genomic library of maize line BE10 (Garst Seed Company, Iowa). This library, 3 × l0 s primary clones, was screened with oligonucleotides complementary to wheat CAB cDNA [5] and the insert of a cucumber CAB cDNA clone [4]. This has permitted the isolation of one genomic clone, gCAB48, containing a 13 kb insert. This clone contained a 2.8 kb PstI fragment which hybridised to the above probes. This fragment was subcloned into pUC19 and the complete sequence determined. This revealed that a complete CAB gene including extensive 5' upstream sequence was contained on this Pst I fragment (Fig. 1). The features of this gene are: 1. The gCAB48 gene does not contain an intron. Therefore, it can be classified as CAB type I. Thus, it is of the same type as the previously published maize gene [9]. 2. The predicted pre-CAB polypeptide sequence consists of 264 amino acids and has a molecular mass of 28 240 kDa. 3. Alignment of gCAB48-encoded protein sequence with other monocotyledonous CAB

The chlorophyll ab complex, CP29, is associated with the Photosystem II reaction centre core

Photosystem II particles from spinach prepared by an octylglucoside method (Ghanotakis et al. (1987) Biochim. Biophys. Acta 891, 15–21) totally lack the antenna chlorophyll-protein complex LHC II, but do contain CP47, CP43 and a third chlorophyll-protein complex, as shown by non-denaturing SDS electrophoresis. This latter core-associated complex is shown to be CP29 on the basis of: (i) the apparent molecular weight of the holocomplex; (ii) the presence of Chi b as well as Chi a in excised gel slices of the complex; and (ii) the cross reaction of the apoproteins with polyclonal antibodies to barley CP29 and with monoclonal antibodies to the N-terminus of the apoprotein of pea CP29. The PS II particles are also enriched in a 23 kDa polypeptide of unknown function.

Modification of the Photosystem II light-harvesting chlorophyll [formula omitted] protein complex in maize during chill-induced photoinhibition

The changes in the functional and molecular organization of the light-harvesting chlorophyll ab protein complex (LHC II), associated with Photosystem II (PS II), are examined when maize leaves are exposed to high light at 5°C for 6 h. Chlorophyll-fluorescence kinetic analyses of thylakoids isolated from mesophyll cells of stressed and control leaves demonstrate that the stress produces a reduction in energy transfer from LHC II to PS II. The polypeptide complements of thylakoids isolated from stressed leaves showed the accumulation of a 31 kDa polypeptide; no other changes in thylakoid polypeptides were observed between control and stress leaves. The 31 kDa polypeptide was a component of purified LHC II from stressed leaves and was immunologically related to the LHC II polypeptides. Differences in fluorescence emission spectra at 77 K of purified LHC II from control and stressed leaves suggested that the stress induces a perturbation of the environment of the chlorophyll species. The appearance of the 31 kDa polypeptide correlated with a modification of LHC II and its functional association with PS II. It is suggested that this polypeptide is a precursor of LHC II polypeptides and is inserted into the membrane prior to processing.