Abstract
Water deficit stress during the reproductive stage considerably obstructs in the desired crop productivity. Camelina sativa is an important oilseed due to its potential in the production of biodiesel and bioproduct. To investigate the water deficit– induced effects and PGPB on the growth and seed composition of Camelina “Soheil cultivar”, an experiment was programmed in three irrigation levels (well water: 100% FC, mild water deficit: 75%FC and severe water deficit: 50%FC) and the presence of Micrococcus yunnanensis as plant growth- promoting bacteria during the reproductive phase. The results showed that under water deficit stress, silique and seed number and silique length decrease provided it coincided with the increase of seed weight. The water deficit resulted in the noticeable alternation in the carbon and nitrogen partitioning to developing seed and subsequently the decrease of oil content associated with the increased protein and total carbohydrate content. Carbon to nitrogen ratio and oil content were in a line in all of the treatment. Additionally, the nitrogen to sulphur ratio positively correlated to protein content. Phosphorous content significantly increased under water deficit stress. In seeds, the increase of Mn associated with the decrease of Fe and Zn was seen when plants treated with drought stress. The obtained results of GC showed that the highest proportion of fatty acid was related to poly unsaturated fatty acid (55.12 to 65.66%) in particular linolenic acid. The increase of poly unsaturated fatty acid and saturated fatty acid coincided with the decrease of mono unsaturated fatty acid under water deficit stress. The antioxidant capacity and total phenol content had an increasing trend with limited water. PGPB application resulted in the increase of weight seed, seed and silique number, nutrients uptake and subsequently the increase of protein. Also, PGPB increased antioxidant capacity and total phenol capacity. PGPB decreased oil content but it had various effects on fatty acid profiles. In general, water deficit stress and PGPB have significant effect on remobilization nutrients from soil to developing seed and following metabolites synthesis
Keywords : water deficit stress, Camelina sativa , plant growth promoting bacteria, fatty acid profile, seed composition.
IntroductionWater deficit stress is a major abiotic threat affecting directly on gene expression, cell metabolism, plant physiology, morphology, and biochemistry feature results in the reduction of plant growth and development and poor crop productivity (Reddy et al., 2004; Guo et al., 2018; You et al., 2018). Water deficit stress during the life cycle particularly in the reproductive stage could encounter plant with a more drastic problem. As, water deficient in seed filling stage were leaded to decline of seed size following disturbance of storage reserves accumulation (Kok et al., 2013). Several studies indicated that the flowering and seed filling stage is the most susceptible stage to water deficit stress (Sehgal et al., 2018). During the reproductive stage, water deficit stress remarkably affects the nutrients allocation and remobilization of photosynthetic assimilates conducing alternation of seed size, seed number, the weight of seed and seed composition (Hussain et al., 2018; Sehgal et al., 2018). The nutrients management strategy is the most major target of the plant to cope with stresses. It is well documented that water deficit effect on the source- to- sink nutrients partitioning in particular nitrogen (N) and carbon (C) during seed development (Durand et al., 2018). In the seed filling stage, carbohydrates (photosynthesis assimilates) in both leaves (Singh et al., 2016) and silique wall (Li et al., 2016; Ni et al., 2019) act as a carbon supply source for developing seed. On the other hand, water stress– accumulated carbohydrates applied for the biosynthesis compatible soluble in developing seeds (Thalmann and Santelia 2017). The various reports indicated that the developing oilseed C: N ratio act as an effective indicator in suitable partitioning of resources for the oil and protein biosynthesis. Additionally, this ratio alters under stress conditions which can be due to the decrease of photosynthesis and the rate increase of seed development (Gan et al., 2004; Hussain et al., 2019; Lee et al., 2020). In oilseeds, C and N content have a strongly positive correlation with oil and protein content respectively. As oil synthesis is parallel with carbon accumulation and nitrogen limitation (Jaradat and Rinke 2010; Calvery et al., 2016). In oilseed corps, sulphur requirement is higher than other crops for the synthesis of proteins containing s-amino acids and s-containing secondary metabolites (Poisoon et al., 2019; Dhillon et al., 2019). Even though sulphur proportion in the seed is considerably lower than nitrogen but its importance is as well as nitrogen as so far as N: S ratio can be suitable indicator assessing of growth and seed yield and its quality (Poisoon et al., 2019). In the last decades, the global change of climate and subsequent drought appearance have become a serious problem and it is important acquiescence to an efficient approach with the object of sustainable agriculture under stress condition. It is well documented that plant growth– promoting bacteria (PGPBs) is an all-purpose option in growth, development, and increase of the crop yield. Also, PGPBs handles biotic and abiotic stress- induced climacteric conditions. PGPB- induced physiological, biochemical and morphological changes in the host result in various mechanisms such as to provide N2 for plants, generation of the plant growth- modulators materials including cytokines, gibberellins, auxins, abscisic acid and ethylene, production of siderophores and higher acquisition to nutrients by solubilization and mineralization (Marulanda et al., 2009; Etesami and Maheshwari, 2018). Some reports have shown the significant effects of PGPB on physical (weight and number seed), and chemical (oil, protein, and mineral elements) trait oilseeds (Olivera et al., 2018; Etesami and Maheshwari, 2018). The antioxidants in oilseed are a determinant indicator of oil stability for oxidative-induced factors. Phenolic compounds possessing multifunction act as important antioxidant (Ali et al., 2012; Kurasiak-Popowska et al., 2019). The importance of oilseeds as one of the essential sources of oil, protein and mineral has been recognized for both of the nutritional and non-nutritional uses (Poisson et al., 2019)Camelina sativa L. Crantz (or false flax) an oilseed crop belonging to the Brassicaceae family has a notable potency for the cultivation in the different climates in the world. Great agronomical attributes of camelina which had lionized in last decades are low- demand nutrients, short- term duration of growth, nutrient retention (Anderson et al., 2019) and high resistance to biotic and abiotic stress (Soorni et al., 2017; Yuan et al., 2017). As for high genetic conservation (≤ 80%) (Lohaus et al., 2020) camelina with Arabidopsis, researchers recognized camelina as a suitable genetic model in the study of genes function and transgenic plants (Heydarian et al., 2016). Camelina seed is a rich source oil, protein and mineral nutrients. Based on obtained studies, camelina oil with the relatively high level of unsaturated fatty acid content (≤85%) and desirable level of erucic acid (≥3%) is highlighted as a superior vegetable oil with multiple potential in the industries such as, feedstock, biodiesel, cosmetic, medicine, and biopolymers (Waraich et al., 2013; Obour et al., 2017; Jankowsky et al., 2019; Wiwart et al., 2019). Although obtained studies showed that, camelina plant is low– demand water and can acclimate to water deficit but there is not information not only on effect water deficit during the reproductive phase but also the effect of PGPB symbiosis on growth, seed quality and seed composition. The objective of the present experiment is to evaluate the effect of water deficit stress on Camelina “Soheil cultivar in 75 and 50% FC levels from bud to seed maturation stage and also the influence of Micrococcus yunnanensis on growth, physical trait seed, protein and oil content, fatty acid profile and some minerals of seed.