A field study on using soybean waste-derived superabsorbent hydrogel to enhance growth of vegetables.

Food security is critical and has become a global concern with many of our basic food crops growing in areas with high drought risk. To improve soil water holding capacity, hydrogels are a promising solution. However, the current ones are mostly derived from petroleum products and are environmental unsustainable. In this study, the main objective is to determine if bio-based hydrogel can help in the growth of leafy vegetables while minimizing water use under field conditions. To achieve this, we developed an okara-derived hydrogel (Ok-PAA; OP) from by-products of bean curd and soybean milk production. We incorporated OP into soil and assessed the growth performance of leafy vegetables. We observed that vegetables grown with 0.2% (w/v) OP in soil with a watering frequency of 7 times per week resulted in >60 % and 35 % yield increase for the common Asian leafy vegetables, choy sum (CS) and pak choi (PC), respectively, as compared to without hydrogel supplementation. Both vegetables produced larger leaf areas (20-40 % increment) in the presence of the hydrogel as compared to those without. In addition, with OP amendment, the irrigation water use efficiency improved >60 % and 30 % for CS and PC, respectively. It is estimated that with the use of the hydrogel, a reduction in watering frequency from 21 times to 7 times per week could be achieved, and based on a per hectare estimation, this would result in 196,000 L of water saving per crop cycle. Statistical analysis and modelling further confirmed vegetables grown with 0.2 % (w/v) OP and with a watering frequency of 7 times per week showed the best growth performance and water use efficiency. Such a waste-to-resource approach offers a plant-based soil supplement for crop growers, contributes to waste valorization, and enhances the growth of plants especially under water-limited conditions.

Nutritional metabolites in Brassica rapa subsp. chinensis var. parachinensis (choy sum) at three different growth stages: Microgreen, seedling and adult plant.

Choy sum is a commonly consumed Asian green leafy brassica vegetable. A comprehensive spectrum of nutritional important metabolites, including amino acids, plant sugars, essential minerals, vitamins (A, B9, E, and K1) and glucosinolates were systematically quantified using LC-QQQ-MS, GC-QQQ-MS and ICP-MS. Significant metabolic profile shifts were observed during the three major developmental stages (microgreen, seedling and adult) studied. Primary metabolites, especially essential amino acids decreased while most plant sugars increased from microgreens to seedlings. Carotenoids, such as violaxanthin, neoxanthin, together with vitamin K1 were higher in the seedlings whereas CHO-folate vitamers and ß-cryptoxanthin were much lower in adult plants. Most essential minerals were concentrated in the microgreens, while sodium increased in adult plants. Aliphatic glucosinolates in microgreens were converted to indolic glucosinolates in the seedlings and further to aromatic glucosinolates in the adults. Overall findings reveal that most of the nutritional metabolites were concentrated either in the microgreens or seedlings.

Chemical Modification of Biomass Okara Using Poly(acrylic acid) through Free Radical Graft Polymerization.

Okara (Ok) or soybean residue is produced as a byproduct from the soybean milk and soybean curd industries world wide, most of which is disposed or burned as waste. It is important to explore the possibilities to convert okara to useful materials, because okara is a naturally renewable bioresource. Here, we report the chemical modification of okara by grafting poly(acrylic acid) (PAA) onto the backbones of okara in water medium and the characterization of the Ok-PAA graft copolymers. It was found that the received okara mainly contained insoluble contents in water. The insoluble okara component Ok(Ins) was suspended in water and activated with ammonium persulfate as an initiator, followed by grafting PAA through a free radical polymerization. After the graft polymerization, the product (Ok-PAA) was separated into precipitate and supernatant, which were dried to give Ok-PAA(pre) and Ok-PAA(sup), respectively. It was found that PAA was grafted on Ok backbones and co-precipitated with the insoluble Ok. In addition, Ok-PAA(sup) was found to be translucent as a result of the grafting of PAA. Further, the successful grafting of PAA onto okara backbones was proven by Fourier transform infrared, thermogravimetric analysis, and microscopic measurements. Ok-PAA(sup) dispersed in water formed nanoparticles with an average diameter of 420 nm, while Ok-PAA(pre) was clustered coarse particles in water. The rheological data including the storage modulus, loss modulus, and viscosity indicated that the Ok-PAA product was a viscoelastic gel-like material with potential for agricultural and environmental applications.

Proteomic Characterisation of the Salt Gland-Enriched Tissues of the Mangrove Tree Species Avicennia officinalis.

Plant salt glands are nature's desalination devices that harbour potentially useful information pertaining to salt and water transport during secretion. As part of the program toward deciphering secretion mechanisms in salt glands, we used shotgun proteomics to compare the protein profiles of salt gland-enriched (isolated epidermal peels) and salt gland-deprived (mesophyll) tissues of the mangrove species Avicennia officinalis. The purpose of the work is to identify proteins that are present in the salt gland-enriched tissues. An average of 2189 and 977 proteins were identified from the epidermal peel and mesophyll tissues, respectively. Among these, 2188 proteins were identified in salt gland-enriched tissues and a total of 1032 selected proteins were categorized by Gene Ontology (GO) analysis. This paper reports for the first time the proteomic analysis of salt gland-enriched tissues of a mangrove tree species. Candidate proteins that may play a role in the desalination process of the mangrove salt glands and their potential localization were identified. Information obtained from this study paves the way for future proteomic research aiming at elucidating the molecular mechanism underlying secretion in plant salt glands. The data have been deposited to the ProteomeXchange with identifier PXD000771.

Proteome profile of salt gland-rich epidermis extracted from a salt-tolerant tree species.

Preparation of proteins from salt-gland-rich tissues of mangrove plant is necessary for a systematic study of proteins involved in the plant's unique desalination mechanism. Extraction of high-quality proteins from the leaves of mangrove tree species, however, is difficult due to the presence of high levels of endogenous phenolic compounds. In our study, preparation of proteins from only a part of the leaf tissues (i.e. salt gland-rich epidermal layers) was required, rendering extraction even more challenging. By comparing several extraction methods, we developed a reliable procedure for obtaining proteins from salt gland-rich tissues of the mangrove species Avicennia officinalis. Protein extraction was markedly improved using a phenol-based extraction method. Greater resolution 1D protein gel profiles could be obtained. More promising proteome profiles could be obtained through 1D-LC-MS/MS. The number of proteins detected was twice as much as compared to TUTS extraction method. Focusing on proteins that were solely present in each extraction method, phenol-based extracts contained nearly ten times more proteins than those in the extracts without using phenol. The approach could thus be applied for downstream high-throughput proteomic analyses involving LC-MS/MS or equivalent. The proteomics data presented herein are available via ProteomeXchange with identifier PXD001691.

Dynamic secretion changes in the salt glands of the mangrove tree species Avicennia officinalis in response to a changing saline environment.

The specialized salt glands on the epidermis of halophytic plants secrete excess salts from tissues by a mechanism that is poorly understood. We examined the salt glands as putative salt and water bi-regulatory units that can respond swiftly to altering environmental cues. The tropical mangrove tree species (Avicennia officinalis) is able to grow under fluctuating salinities (0.7-50.0 dS m(-1)) at intertidal zones, and its salt glands offer an excellent platform to investigate their dynamic responses under rapidly changing salinities. Utilizing a novel epidermal peel system, secretion profiles of hundreds of individual salt glands examined revealed that these glands could secrete when exposed to varying salinities. Notably, rhythmic fluctuations observed in secretion rates were reversibly inhibited by water channel (aquaporin) blocker, and two aquaporin genes (PIP and TIP) preferentially expressed in the salt gland cells were rapidly induced in response to increasing salt concentration. We propose that aquaporins are involved and contribute to the re-absorption of water during salt removal in Avicennia officinalis salt glands. This constitutes an adaptive feature that contributes to salt balance of trees growing in saline environments where freshwater availability is limited.

A simple, rapid method to isolate salt glands for three-dimensional visualization, fluorescence imaging and cytological studies.

BACKGROUND: Some plants inhabiting saline environment remove salts via the salt glands embedded in the epidermal tissues. Cytological studies of salt glands will provide valuable information to our understanding of the secretory process. Previous studies on salt gland histology relied mainly on two-dimensional microscopic observations of microtome sections. Optical sectioning properties of confocal laser scanning microscope offer alternative approach for obtaining three-dimensional structural information of salt glands. Difficulty in light penetration through intact leaves and interference from neighbouring leaf cells, however, impede the acquiring of good optical salt gland sections and limit its applications in salt gland imaging. Freeing the glands from adjacent leaf tissues will allow better manipulations for three-dimensional imaging through confocal laser scanning microscopy. RESULTS: Here, we present a simple and fast method for the isolation of individual salt glands released from the interference of neighbouring cells. About 100-200 salt glands could be isolated from just one cm2 of Avicennia officinalis leaf within hours and microscopic visualization of isolated salt glands was made possible within a day. Using these isolated glands, confocal laser scanning microscopic techniques could be applied and better resolution salt gland images could be achieved. By making use of their intrinsic fluorescent properties, optical sections of the gland cells could be acquired without the use of fluorescent probes and the corresponding three-dimensional images constructed. Useful cytological information of the salt gland cells could also be obtained through the applications of fluorescent dyes (e.g., LysoTracker® Red, FM®4-64, Texas Red®). CONCLUSIONS: The study of salt glands directly at the glandular level are made possible with the successful isolation of these specialized structures. Preparation of materials for subsequent microscopic observations of salt glands could be achieved within a day. Potential applications of confocal fluorescence microscopic techniques could also be performed using these isolated glands. Experiments designed and targeted directly at the salt glands were explored and cytological information obtained herein could be further incorporated towards the understanding of the mechanism underlying secretion in plant salt glands.