Developmental age is a strong determinant of stress responses in plants. Differential susceptibility to various environmental stresses is widely observed at both the organ and whole-plant level. While it is clear that age determines stress susceptibility, the causes, regulatory mechanisms, and functions are only now beginning to emerge. Compared with concepts on age-related biotic stress resilience, advancements in the abiotic stress field are relatively limited. In this review, we focus on current knowledge of ontogenic resistance to abiotic stresses, highlighting examples at the organ (leaf) and plant level, preceded by an overview of the relevant concepts in plant aging. We also discuss age-related abiotic stress resilience mechanisms, speculate on their functional relevance, and outline outstanding questions. The Concept of AgingThe definitions of plant aging (see Glossary) are diverse. One might think of aging to comprehend the entire plant life cycle: from seed to senescence. However, this cycle is different for annuals and perennials. Annuals and biennials are semelparous (monocarpic) species that undergo their complete life cycle in one or two growing seasons, respectively. Perennials are iteroparous (polycarpic) species that live for many years with a clear disjunction between plant and organ lifespan. In this review, we mainly focus on age-related aspects of annuals, but some concepts are equivalent to specific organs of perennials that undergo repeated yearly cycles. HighlightsThe processes of aging, such as leaf development, senescence, and phase transitions from juvenile to adult plants, are genetically programmed and highly controlled by complex regulatory pathways.During aging, plants alter their organ morphology, sink-source balances, and chemical composition, including changes in redox status and hormone levels, which will collectively determine how abiotic stress signals are perceived and processed.

Nowadays, genome editing tools are indispensable for studying gene function in order to increase our knowledge of biochemical processes and disease mechanisms. The extensive availability of mutagenesis and transgenesis tools make Drosophila melanogaster an excellent model organism for geneticists. Early mutagenesis tools relied on chemical or physical methods, ethyl methane sulfonate (EMS) and X-rays respectively, to randomly alter DNA at a nucleotide or chromosomal level. Since the discovery of transposable elements and the availability of the complete fly genome, specific genome editing tools, such as P-elements, zinc-finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs), have undergone rapid development. Currently, one of the leading and most effective contemporary tools is the CRISPR-cas9 system made popular because of its low cost, effectiveness, specificity and simplicity of use. This review briefly addresses the most commonly used mutagenesis and transgenesis tools in Drosophila, followed by an in-depth review of the multipurpose CRISPR-Cas9 system and its current applications.

Salt stress hampers plant growth and development through both osmotic and ionic imbalances. One of the key players in modulating physiological responses towards salinity is the plant hormone abscisic acid (ABA). How plants cope with salinity largely depends on the magnitude of the soil salt content (stress severity), but also on age-related developmental processes (ontogeny). Here we studied how ABA directs salt stress responses in tomato plants for both mild and severe salt stress in leaves of different ages. We used the ABA-deficient mutant notabilis, which contains a null-mutation in the gene of a rate-limiting ABA biosynthesis enzyme 9-cis-epoxycarotenoid dioxygenase (NCED1), leading to impaired stomatal closure. We showed that both old and young leaves of notabilis plants keep a steady-state transpiration and photosynthesis rate during salt stress, probably due to their dysfunctional stomatal closure. At the whole plant level, transpiration declined similar to the wild-type, impacting final growth. Notabilis leaves were able to produce osmolytes and accumulate ions in a similar way as wild-type plants, but accumulated more proline, indicating that osmotic responses were not impaired by the NCED1 mutation. Besides NCED1, also NCED2 and NCED6 are strongly upregulated under salt stress, which could explain why the notabilis mutant did not show a lower ABA content upon salt stress, except in young leaves. This might be indicative of a salt-mediated feedback mechanism on NCED2/6 in notabilis and might explain why notabilis plants seem to perform better under salt stress compared to wild-type plants with respect to biomass and water content accumulation.

Diffuse greenhouse glass can increase the production and growth of several crops, by scattering the incoming direct sunlight, which results in a better and more homogeneous light distribution in the crop canopy. Tomato and bell pepper growers in Belgium tend to install low-haze diffuse glass with a double anti-reflection (AR) coating. These glass types have a limited diffuse effect but have a higher light transmission compared to standard float glass. Therefore, tomato growers often increase stem density to maximize light interception. However, a denser crop could counteract the positive effects of diffuse glass on the vertical light distribution. In this study, the effect of low-haze diffuse glass with an AR coating was evaluated for different cropping densities for tomato and bell pepper taking into account the vertical light distribution throughout the crop canopy. Tomato plants with two stem densities (3.33 and 3.75 stems.m−2) and bell pepper plants (with only one stem density of 7.1 stems.m−2) were evaluated in a greenhouse compartment with diffuse and reference float glass during a full growing season. For tomato, a significant production increase of 7.5% was observed under diffuse glass during the second half of the growing season but only for the low stem density. The benefit of diffuse glass appears most relevant during sunny clear skies and on the sun-side-facing rows of the crop. For bell pepper, no significant production increases were noted between regular float or diffuse glass, because a bell pepper crop is typically covered with thermal screens to prevent sunburn on the fruits during sunny days. The vertical light distribution and the usefulness of AR-coated diffuse glass depends on the crop type and should be optimized accordingly by altering the stem density, leaf pruning strategy, row orientation, or crop variety.