Polyhydroxyalkanoates (PHAs) make a large class of biodegradable biopolymers that are naturally synthesized by numerous microorganisms. These biopolymers could be an alternative to commonly used plastics based on petroleum. Production of PHAs in bioreactors using microorganisms is not widely applied due to its unprofitability. Using transgenic plants for this purpose may be cheaper and more environmental friendly because the biosynthesis of PHAs in plants is based only on water, mineral salts, CO₂ and light. Additionally, plants are not capable of degrading PHAs as bacteria do, and extraction of PHAs from plant tissues is not always necessary. The main objective of this work is a review of possibilities of PHA biosynthesis in transgenic plants and presentation of general information on properties and potential application possibilities of these biopolymers. The possibility of syntheses and accumulation of PHA in several transgenic plants has been studied for some years. Many experiments were performed on model plant Arabidopsis thaliana, however, the research has also revealed a great potential of transgenic crop plants such as camelina (Camelina sativa), tobacco (Nicotiana tabacum) or sugarcane (Saccharum officinarum) as a good sources of PHAs. The highest level of PHAs accumulation in plants was achieved in transgenic A. thaliana (up to 40% of the dry weight of the leaf), and among crop plants in C. sativa (up to 20% of the dry weight of the seed). Increasing knowledge on PHAs permits expansion of the possibilities of these biopolymers use even at a low level of their accumulation in plant tissues.

Vacuolar processing enzymes (VPEs) are plant cysteine proteases that are subjected to autoactivation in an acidic pH. It is presumed that VPEs, by activating other vacuolar hydrolases, are in control of tonoplast rupture during programmed cell death (PCD). Involvement of VPEs has been indicated in various types of plant PCD related to development, senescence, and environmental stress responses. Another pathway induced during such processes is autophagy, which leads to the degradation of cellular components and metabolite salvage, and it is presumed that VPEs may be involved in the degradation of autophagic bodies during plant autophagy. As both PCD and autophagy occur under similar conditions, research on the relationship between them is needed, and VPEs, as key vacuolar proteases, seem to be an important factor to consider. They may even constitute a potential point of crosstalk between cell death and autophagy in plant cells. This review describes new insights into the role of VPEs in plant PCD, with an emphasis on evidence and hypotheses on the interconnections between autophagy and cell death, and indicates several new research opportunities.

A comparative study was carried out on the dynamics of lipid accumulation in developing seeds of three lupine species. Lupine seeds differ in lipid content; yellow lupine (Lupinus luteus L.) seeds contain about 6%, white lupine (Lupinus albus L.) 7–14%, and Andean lupine (Lupinus mutabilis Sweet) about 20% of lipids by dry mass. Cotyledons from developing seeds were isolated and cultured in vitro for 96 h on Heller medium with 60 mM sucrose (+S) or without sucrose (–S). Each medium was additionally enriched with 35 mM asparagine or 35 mM NaNO₃. Asparagine caused an increase in protein accumulation and simultaneously decreased the lipid content, but nitrate increased accumulation of both protein and lipid. Experiments with [1-¹⁴C]acetate and [2-¹⁴C]acetate showed that the decrease in lipid accumulation in developing lupine seeds resulted from exhaustion of lipid precursors rather than from degradation or modification of the enzymatic apparatus. The carbon atom from the C-1 position of acetate was liberated mainly as CO₂, whereas the carbon atom from the C-2 position was preferentially used in anabolic pathways. The dominant phospholipid in the investigated lupine seed storage organs was phosphatidylcholine. The main fatty acid in yellow lupine cotyledons was linoleic acid, in white lupine it was oleic acid, and in Andean lupine it was both linoleic and oleic acids. The relationship between stimulation of lipid and protein accumulation by nitrate in developing lupine cotyledons and enhanced carbon flux through glycolysis caused by the inorganic nitrogen form is discussed.

New players in plant signaling are described in detail in this review: extracellular ATP (eATP) and uncommon nucleotides such as dinucleoside polyphosphates (Np_nN’s), adenosine 5′-phosphoramidate (NH₂-pA), and extracellular NAD⁺ and NADP⁺ (eNAD(P)⁺). Recent molecular, physiological, and biochemical evidence implicating concurrently the signaling role of eATP, Np_nN’s, and NH₂-pA in plant biology and the mechanistic events in which they are involved are discussed. Numerous studies have shown that they are often universal signaling messengers, which trigger a signaling cascade in similar reactions and processes among different kingdoms. We also present here, not described elsewhere, a working model of the Np_nN’ and NH₂-pA signaling network in a plant cell where these nucleotides trigger induction of the phenylpropanoid and the isochorismic acid pathways yielding metabolites protecting the plant against various types of stresses. Through these signals, the plant responds to environmental stimuli by intensifying the production of various compounds, such as anthocyanins, lignin, stilbenes, and salicylic acid. Still, more research needs to be performed to identify signaling networks that involve uncommon nucleotides, followed by omic experiments to define network elements and processes that are controlled by these signals.

The main storage compound in lupin seeds is protein, whose content can reach up to 45–50 % of dry matter. However, seeds of some lupin species can also contain quite a large amount of storage lipid. The range of lipid content in lupin seeds is from about 6 to about 20 % of dry matter. Storage lipid in developing seeds is synthesized mainly from sugars delivered by mother plants. During seed germination, one of the main end-products of storage lipid breakdown is also sugars. Thus, the sugar level in tissues is considered an important regulatory agent, during both lipid accumulation and lipid breakdown. Generally, in developing legume seeds, there is a strong negative relation between accumulation of storage protein and storage lipid. Results obtained in developing lupin cotyledons cultured in vitro pointed to the possibility of a positive relation between protein and lipid accumulation. Such a positive effect could be caused by nitrate. During lupin seed germination and seedling development, the utilization of storage lipid is enhanced under sugar deficiency conditions in tissues and is controlled at the gene expression level. However, under sugar starvation conditions, autophagy is significantly enhanced, and it can cause disturbances in storage lipid breakdown. The hypothesis of pexophagy, i.e., autophagic degradation of peroxisomes under sugar starvation conditions during lupin seed germination, has been taken into consideration. The flow of lipid-derived carbon skeletons to amino acids was discovered in germinating lupin seeds, and this process is clearly more intense in sucrose-fed embryo axes. At least four alternative or mutually complementary pathways of carbon flow from storage lipid to amino acids in germinating lupin seeds are postulated. The different strategies of storage compound breakdown during lupin seed germination are also discussed.