Main conclusion: Shoot tip necrosis is a physiological condition that negatively impacts the growth and development of in vitro plant shoot cultures across a wide range of species. Shoot tip necrosis is a physiological condition and disorder that can arise in plantlets or shoots in vitro that results in death of the shoot tip. This condition, which can spread basipetally and affect the emergence of axillary shoots from buds lower down the stem, is due to the cessation of apical dominance. STN can occur at both shoot multiplication and rooting stages. One of the most common factors that cause STN is nutrient deficiency or imbalance. Moreover, the presence or absence of plant growth regulators (auxins or cytokinins) at specific developmental stages may impact STN. The cytokinin to auxin ratio within an in vitro plant can be modified by varying the concentration of cytokinins used in the culture medium. The supply of nutrients to in vitro shoots or plantlets might also affect their hormonal balance, thus modifying the occurrence of STN. High relative humidity within culture vessels and hyperhydricity are associated with STN. An adequate supply of calcium as the divalent cation (Ca²⁺) can hinder STN by inhibiting the accumulation of phenolic compounds and thus programmed cell death. Moreover, the level of Ca²⁺affects auxin transport and ethylene production, and higher ethylene production, which can occur as a result of high relative humidity in or poor ventilation of the in vitro culture vessel, induces STN. High relative humidity can decrease the mobility of Ca²⁺within a plant, resulting in Ca²⁺deficiency and STN. STN of in vitro shoots or plantlets can be halted or reversed by altering the basal medium, mainly the concentration of Ca²⁺, adjusting the levels of auxins or cytokinins, or modifying culture conditions. This review examines the literature related to STN, seeks to discover the associated factors and relations between them, proposes practical solutions, and attempts to better understand the mechanism(s) underlying this condition in vitro.

1 Peatland soils are estimated to store a third of all terrestrial carbon stocks and are very sensitive to climate change. In these systems, one group of soil mesofauna, enchytraeid worms (Annelida, Oligochaeta), represent up to 70% of total soil fauna biomass and previous studies have highlighted their potential use as ‘biological indicators’ for functionally important changes in the C cycle. 2 To examine the link between temperature, enchytraeids and carbon fluxes we performed a microcosm experiment in which we assessed the influence of temperature on enchytraeid populations and soil CO₂ and DOC release from a Galician peatland soil over 90 days. Additionally, to unravel the potential underlying mechanisms responsible for DOC production, we also tested the effects of increasing temperatures and enchytraeid activities on the presence of organic chelating metals (iron and aluminium) and hydrogen ions (i.e. acidity) in the soil solution. 3 Enchytraeid population numbers and biomass increased over time at both temperature treatments (14 and 19 °C), with the greatest increase produced at the highest temperature (to over five and seven times higher initial values, respectively, by day 88). Results also showed that, under warmer conditions, enchytraeid activities increased both CO₂ fluxes and DOC release by twofold (Q₁₀ values of 3·9 and 3·6, respectively). 4 The combined effect of temperature and enchytraeids promoted the breakdown of organic substances and consequently, more DOC and iron were leached. An important decline in H⁺ release was observed when enchytraeids were present and possibly eliminating one of the critical mechanisms restricting DOC release. These leachate pH values were also responsible for aluminium immobilisation and hence for its insignificant role in the export of DOC from the peat soil. 5 We conclude that temperature change alone does not explain all the observed increases in soil respiration and DOC production but rather soil invertebrate responses to warming are crucial in controlling C fluxes in peatland soils. This is the result of temperature induced changes of enchytraeid populations and activities which have the potential of speeding up the decomposition of organic matter and altering soil aeration, metal mobilization and acidity of the soil solution, with important implications for the global carbon cycle. 6 There is an urgent need for incorporating the response of soil biology in climate change modelling to make better predictions of future changes in terrestrial carbon pools.

In the last decade, the worldwide production of kiwi fruit has been highly affected by Pseudomonas syringae pv. actinidiae (Psa), a phytopathogenic bacterium; this has led to severe economic losses that are seriously affecting the kiwi fruit trade. The available treatments for this disease are still scarce, with the most common involving frequently spraying the orchards with copper derivatives, in particular cuprous oxide (Cu₂O). However, these copper formulations should be avoided due to their high toxicity; therefore, it is essential to search for new approaches for controlling Psa. Antimicrobial photodynamic therapy (aPDT) may be an alternative approach to inactivate Psa. aPDT consists in the use of a photosensitizer molecule (PS) that absorbs light and by transference of the excess of energy or electrons to molecular oxygen forms highly reactive oxygen species (ROS) that can affect different molecular targets, thus being very unlikely to lead to the development of microbe resistance. The aim of the present study was to evaluate the effectiveness of aPDT to photoinactivate Psa, using the porphyrin Tetra-Py⁺-Me and different light intensities. The degree of inactivation of Psa was assessed using the PS at 5.0 μM under low irradiance (4.0 mW cm⁻²). Afterward, ex vivo experiments, using artificially contaminated kiwi leaves, were conducted with a PS at 50 μM under 150 mW cm⁻² and sunlight irradiation. A reduction of 6 log in the in vitro assays after 90 min of irradiation was observed. In the ex vivo tests, the decrease was lower, approximately 1.8 log reduction at an irradiance of 150 mW cm⁻², 1.2 log at 4.0 mW cm⁻², and 1.5 log under solar radiation. However, after three successive cycles of treatment under 150 mW cm⁻², a 4 log inactivation was achieved. No negative effects were observed on leaves after treatment. Assays using Cu₂O were also performed at the recommended concentration by law (50 g h L⁻¹) and at concentrations 10 times lower, in which at both concentrations, Psa was efficiently inactivated (5 log inactivation) after a few minutes of treatment, but negative effects were observed on the leaves after treatment.

Many endangered plants such as Eryngium viviparum (Apiaceae) present a poor germination rate. This fact could be due to intrinsic and extrinsic seed variability influencing germination and dormancy of seeds. The objective of this study is to better understand the physiological mechanism of seed latency and, through artificial intelligence models, to determine the factors that stimulate germination rates of E. viviparum seeds. This description could be essential to prevent the disappearance of endangered plants. Germination in vitro was carried out under different dormancy breaking and incubation procedures. Percentages of germination, viability and E:S ratio were calculated and seeds were dissected at the end of each assay to describe embryo development. The database obtained was modeled using neurofuzzy logic technology. We have found that the most of Eryngium seeds (62.6%) were non-viable seeds (fully empty or without embryos). Excluding those, we have established the germination conditions to break seed dormancy that allow obtaining a real germination rate of 100%. Advantageously, the best conditions pointed out by neurofuzzy logic model for embryo growth were the combination of 1 mg L⁻¹ GA₃ (Gibberellic Acid) and high incubation temperature and for germination the combination of long incubation and short warm stratification periods. Our results suggest that E. viviparum seeds present morphophysiological dormancy, which reduce the rate of germination. The knowledge provided by the neurofuzzy logic model makes possible not just break the physiological component of dormancy, but stimulate the embryo development increasing the rate of germination. Undoubtedly, the strategy developed in this work can be useful to recover other endangered plants by improving their germination rate and uniformity favoring their ex vitro conservation.