Maziah Mahmood

Water stress-induced oxidative damage and antioxidant responses in micropropagated banana plantlets

Oxidative injury and antioxidant responses were investigated in two banana genotypes (Musa AAA ‘Berangan’ and Musa AA ‘Mas’) subjected to 40 % PEG-induced water stress. PEG treatment resulted in oxidative injury, as expressed in increased lipid peroxidation and reduced membrane stability index, in both cultivars; however, greater oxidative injury was detected in ‘Mas’. Under PEG treatment, catalase activity and glutathione reductase activity were enhanced in both cultivars, but were higher in ‘Mas’. Ascorbate peroxidase activity was enhanced in ‘Berangan’ under water stress, but was unaffected in ‘Mas’. Meanwhile, superoxide dismutase activity was inhibited in both cultivars under water stress, but higher activity was detected in ‘Berangan’. Higher ascorbate peroxidase and superoxide dismutase activities were associated with greater protection against water stress-induced oxidative injury.

Marker-assisted backcrossing: a useful method for rice improvement

The worlds population is increasing very rapidly, reducing the cultivable land of rice, decreasing table water, emerging new diseases and pests, and the climate changes are major issues that must be addressed to researchers to develop sustainable crop varieties with resistance to biotic and abiotic stresses. However, recent scientific discoveries and advances particularly in genetics, genomics and crop physiology have opened up new opportunities to reduce the impact of these stresses which would have been difficult if not impossible as recently as the turn of the century. Marker assisted backcrossing (MABC) is one of the most promising approaches is the use of molecular markers to identify and select genes controlling resistance to those factors. Regarding this, MABC can contribute to develop resistant or high-yielding or quality rice varieties by incorporating a gene of interest into an elite variety which is already well adapted by the farmers. MABC is newly developed efficient tool by which using large population sizes (400 or more plants) for the backcross F1 generations, it is possible to recover the recurrent parent genotype using only two or three backcrosses. So far, many high yielding, biotic and abiotic stresses tolerance, quality and fragrance rice varieties have been developed in rice growing countries through MABC within the shortest timeframe. Nowadays, MABC is being used widely in plant breeding programmes to develop new variety/lines especially in rice. This paper reviews recent literature on some examples of variety/ line development using MABC strategy.

Alleviation of Water Stress Effects on MR220 Rice by Application of Periodical Water Stress and Potassium Fertilization

The use of periodical water stress and potassium fertilization may enhance rice tolerance to drought stress and improve the crop’s instantaneous water use efficiency without much yield reduction. This study was conducted to assess the effects of different periodical water stress combined with potassium fertilization regimes on growth, yield, leaf gas exchanges and biochemical changes in rice grown in pots and compare them with standard local rice grower practices. Five treatments including (1) standard local grower’s practice (control, 80CF = 80 kg K2O/ha + control flooding); (2) 120PW15 = 120 kg K2O/ha + periodical water stress for 15 days; (3) 120DS15V = 120 kg K2O/ha + drought stress for 15 days during the vegetative stage; (4) 120DS25V = 120 kg K2O/ha + drought stress for 25 days and (5) 120DS15R = 120 kg K2O/ha + drought stress for 15 days during the reproductive stage, were evaluated in this experiment. Control and 120PW15 treatments were stopped at 100 DAS, and continuously saturated conditions were applied until harvest. It was found that rice under 120PW15 treatment showed tolerance to drought stress evidenced by increased water use efficiency, peroxidase (POX), catalase (CAT) and proline levels, maximum efficiency of photosystem II (fv/fm) and lower minimal fluorescence (fo), compared to other treatments. Path coefficient analysis revealed that most of parameters contribute directly rather than indirectly to rice yield. In this experiment, there were four factors that are directly involved with rice yield: grain soluble sugar, photosynthesis, water use efficiency and total chlorophyll content. The residual factors affecting rice yield are observed to be quite low in the experiment (0.350), confirming that rice yield was mostly influenced by the parameters measured during the study.

Effect of Plasmolysis on Protocorm-Like Bodies of Dendrobium Bobby Messina Orchid Following Cryopreservation with Encapsulation–Dehydration Method

Histological observation and scanning electron microscopy analyses in Dendrobium Bobby Messina indicates the cellular process of cryopreserved protocorm-like bodies (PLBs) was different comparative to non-cryopreserved PLBs. The cellular process was not only modified by the freezing and thawing effect but also due to the dehydration process itself during the cryopreservation procedure. Histological observation in Dendrobium Bobby Messina in encapsulation–dehydration method indicated that the degree of plasmolysis causes more cellular changes to the cryopreserved PLBs comparative to non-cryopreserved and stock culture PLBs. These results revealed higher amount of homogenous cell population and denser cytoplasm in cryopreserved PLBs. Histological analysis also revealed more voluminous nucleus in cryopreserved PLBs comparative to non-cryopreserved PLBs and PLBs stock culture. In contrast, scanning electron microscope analysis showed severe damages in cryopreserved PLBs and non-cryopreserved PLBs comparative to the PLBs stock culture which in return could be the possible reason of no regrowth in encapsulation–dehydration method. Damages incurred were on top part, side part, and at the stomata of the PLBs. Histological observation and scanning electron microscopy analyses in Dendrobium Bobby Messina indicates that the degree of plasmolysis causes changes in the cellular process of PLBs from cryopreserved PLBs was different comparative to non-cryopreserved PLBs.

Differential Gene Expression Reflects Morphological Characteristics and Physiological Processes in Rice Immunity against Blast Pathogen Magnaporthe oryzae.

The rice blast fungus Magnaporthe oryzae is a serious pathogen that jeopardises the world’s most important food-security crop. Ten common Malaysian rice varieties were examined for their morphological, physiological and genomic responses to this rice blast pathogen. qPCR quantification was used to assess the growth of the pathogen population in resistant and susceptible rice varieties. The chlorophyll content and photosynthesis were also measured to further understand the disruptive effects that M. oryzae has on infected plants of these varieties. Real-time PCR was used to explore the differential expression of eight blast resistance genes among the ten local varieties. Blast disease has destructive effects on the growth of rice, and the findings of our study provide evidence that the Pikh, Pi9, Pi21, and Osw45 genes are involved in defence responses in the leaves of Malaysian rice at 31 h after inoculation with M. oryzae pathotype P7.2. Both the chlorophyll content and photosynthesis were reduced, but the levels of Pikh gene expression remained constant in susceptible varieties, with a developed pathogen population and mild or severe symptoms. The Pi9, Pi21, and Osw45 genes, however, were simultaneously upregulated in infected rice plants. Therefore, the presence of the Pikh, Pi9, Pi21, and Osw45 genes in the germplasm is useful for improving the resistance of rice varieties.

Introgression of blast resistance genes into the elite rice variety MR263 through marker-assisted backcrossing

BACKGROUND Blast caused by the fungus Magnaporthe oryzae is a significant disease threat to rice across the world and is especially prevalent in Malaysia. An elite, early-maturing, high-yielding Malaysian rice variety, MR263, is susceptible to blast and was used as the recurrent parent in this study. To improve MR263 disease resistance, the Pongsu Seribu 1 rice variety was used as donor of the blast resistance Pi-7(t), Pi-d(t)1 and Pir2-3(t) genes and qLN2 quantitative trait locus (QTL). The objective was to introgress these blast resistance genes into the background of MR263 using marker-assisted backcrossing with both foreground and background selection. RESULTS Improved MR263-BR-3-2, MR263-BR-4-3, MR263-BR-13-1 and MR263-BR-26-4 lines carrying the Pi-7(t), Pi-d(t)1 and Pir2-3(t) genes and qLN2 QTL were developed using the simple sequence repeat (SSR) markers RM5961 and RM263 (linked to the blast resistance genes and QTL) for foreground selection and a collection of 65 polymorphic SSR markers for background selection in backcrossed and selfed generations. A background analysis revealed that the highest rate of recurrent parent genome recovery was 96.1% in MR263-BR-4-3 and 94.3% in MR263-BR-3-2. CONCLUSION The addition of blast resistance genes can be used to improve several Malaysian rice varieties to combat this major disease.

Exogenous proline significantly affects the plant growth and nitrogen assimilation enzymes activities in rice (Oryza sativa) under salt stress

Salinity has been shown to be a major factor contributing to low nitrogen availability in plants. To verify the changes in nitrogen metabolism activity as affected by the exogenous application of proline under salt stress and its relation to salt tolerance, in vitro rice shoot apices were used as a model to study the growth performance and changes in nitrogen assimilation activities in two Malaysian rice cultivars MR 220 and MR 253. Results revealed that salt stress greatly reduced the plant height, shoot nitrate (NO3−) content, shoot glutamine synthetase (GS), and root nitrate reductase (NR) activities in both cultivars. Supplementation of proline significantly increased the plant height, number of roots, root NO3− content, root NR, and root GS activities under salt stress in both cultivars with greater enhancement in MR 253 than MR 220. The results also indicated that MR 253 possessed higher nitrite reductase (NiR) and glutamate synthase (NADH–GOGAT) activities as compared with MR 220 in all tested treatments. It was suggested that the NO3− content, NR, and GS activities played important roles in regulating nitrogen metabolism under salt stress. Taken together, it was concluded that the ability of proline in mitigating salt stress-induced damages was correlated with the changes in nitrogen assimilation activities.

Gene expression of the oil palm transcription factor EgAP2-1 during fruit ripening and in response to ethylene and ABA treatments.

A cDNA encoding an ERE-binding protein (EgAP2-1) was isolated from the oil palm fruit mesocarp treated with ethylene using yeast one-hybrid assay. EgAP2-1 belongs to the AP2 subfamily of the APETALA2/ethylene-responsive factor (AP2/ERF) proteins and contains two highly conserved AP2/EREBP DNA-binding domains (DNA-BD). Sequence comparison of EgAP2-1 with other AP2 proteins revealed high conservation of the two AP2/EREBP domains and linker region among these proteins. Its protein was localized to the nucleus of onion epidermis cells and showed ERE-specific binding, transcriptional activation, and transactivation properties in yeast and in vitro. Its mRNA was highly expressed in oil palm mesocarp with elevated levels in ripening fruits but not in leaves and roots. EgAP2-1 was induced in mesocarp in response to ethylene and abscisic acid but not other hormonal stimuli, including methyl jasmonate and salicylic acid, and abiotic stresses including drought, cold, and high-salinity. Our results demonstrate a link between the regulation of EgAP2-1 expression and ethylene- and/or ABA-coordinated control of the fruit ripening and suggest a regulatory role for EgAP2-1 during fruit ripening and development in oil palm.

The Phenylpropanoid Pathway and Lignin in Defense against Ganoderma boninense Colonized Root Tissues in Oil Palm (Elaeis guineensis Jacq.)

Basal stem rot, caused by the basidiomycete fungus, Ganoderma boninense, is an economically devastating disease in Malaysia. Our study investigated the changes in lignin content and composition along with activity and expression of the phenylpropanoid pathway enzymes and genes in oil palm root tissues during G. boninense infection. We sampled control (non-inoculated) and infected (inoculated) seedlings at seven time points [1, 2, 3, 4, 8, and 12 weeks post-inoculation (wpi)] in a randomized design. The expression profiles of phenylalanine ammonia lyase (PAL), cinnamyl alcohol dehydrogenase (CAD), and peroxidase (POD) genes were monitored at 1, 2, and 3 wpi using real-time quantitative polymerase chain reaction. Seedlings at 4, 8, and 12 wpi were screened for lignin content, lignin composition, enzyme activities (PAL, CAD, and POD), growth (weight and height), and disease severity (DS). Gene expression analysis demonstrated up-regulation of PAL, CAD, and POD genes in the infected seedlings, relative to the control seedlings at 1, 2, and 3 wpi. At 2 and 3 wpi, CAD showed highest transcript levels compared to PAL and POD. DS increased progressively throughout sampling, with 5, 34, and 69% at 4, 8, and 12 wpi, respectively. Fresh weight and height of the infected seedlings were significantly lower compared to the control seedlings at 8 and 12 wpi. Lignin content of the infected seedlings at 4 wpi was significantly higher than the control seedlings, remained elicited with no change at 8 wpi, and then collapsed with a significant reduction at 12 wpi. The nitrobenzene oxidation products of oil palm root lignin yielded both syringyl and guaiacyl monomers. Accumulation of lignin in the infected seedlings was in parallel to increased syringyl monomers, at 4 and 8 wpi. The activities of PAL and CAD enzymes in the infected seedlings at DS = 5–34% were significantly higher than the control seedlings and thereafter collapsed at DS = 69%.

Highly efficient protocol for callogenesis, somagenesis and regeneration of Indica rice plants

In the present study, we have reported a simple, fast and efficient regeneration protocol using mature embryos as explants, and discovered its effective applicability to a range of Indica rice genotypes. We have considered the response of six varieties in the steps of the regeneration procedure. The results showed that calli were variably developed from the scutellar region of seeds and visible within 6-20 days. The highest and lowest calli induction frequency (70% and 51.66%) and number of induced calli from seeds (14 and 10.33) were observed in MR269 and MRQ74, respectively. The maximum and minimum number (7.66 and 4) and frequency of embryogenic calli (38.33% and 20%) were recorded in MR219 and MRQ74, respectively. However, the highest browning rate was observed in MR84 (87%) and the lowest rate in MRQ50 (46%). The majority of plants regenerated from embryogenic calli were obtained from MRQ50 (54%) and the minimum number of plants from MR84. In this study, the maximum numbers of plantlets were regenerated from the varieties with highest rate of embryogenic calli. Also, various varieties, including MRQ50, MR269, MR276 and MR219, were satisfactorily responding, while MRQ74 and MR84 weakly responded to the procedure. Such a simple, successful and generalized method possesses the potential to become an important tool for crop improvement and functional studies of genes in rice as a model monocot plant.