ALBERT

Description: Population growth and increased stress caused by urbanization have led to social problems that are predicted to intensify in the future. In these conditions, the recently established ”nature therapy” has revealed that an environment rich in various plant life significantly contributes to the relief of physical and mental stress. Meanwhile, from the perspective of reduction in the energy required for transportation and the retention of plant freshness, urban horticulture, in which plant life exists harmoniously with the city, has attracted considerable attention. Interactions between humans and plants in urban horticulture are considered to contribute to the good health and wellbeing of people. Therefore, we incorporate human-centered thinking based on nature therapy into horticultural produce-centered thinking based on conventional urban horticulture. By introducing a pioneering urban horticulture plant factory as an example, we propose the possibility of sustainable urban horticulture based on nature therapy.

Description: In lisianthus cultivars, the occurrence of tipburn is known to adversely affect quality and yield. However, information concerning the responses of tipburn incidence to different levels of Ca is limited. In addition, only a few studies have investigated the effect of potassium (K) concentration on Ca acquisition and distribution in lisianthus. To address this knowledge gap, we investigated tipburn incidence in three lisianthus cultivars (Umi honoka (UH), Reina white (RW), and Voyage peach (VP)) and the Ca and K concentrations in them under different concentrations of Ca supply (40, 80, and 120 ppm). These cultivars exhibited different responses to different concentrations of Ca supply. Tipburn was not observed in UH. In RW, tipburn incidence and severity significantly decreased with an increase in nutritional Ca concentration, because the Ca concentration in the tips of the top leaves significantly increased with Ca concentration. By contrast, in VP, tipburn incidence under all treatments was 100%, and there was no significant difference in the Ca concentration in the tips of the top leaves among the treatments, but the total Ca concentration significantly increased. VP was the only cultivar that significantly acquired and accumulated more Ca in the roots with an increase in nutritional Ca concentration. Overall, excessive Ca accumulation in the roots under high-Ca conditions inhibits the distribution of Ca to the tips of the top leaves and eventually manifests as tipburn in the cultivar. In addition, our results suggested that the content ratio of K in the nutrient solutions did not prevent Ca acquisition and distribution in lisianthus cultivars and that the K concentration has a negligible effect on the occurrence of tipburn.

Description: Tipburn is a major problem for the production of lisianthus (Eustoma grandiflorum (Raf.) Shinn.) cultivars. Relative air humidity is regarded as a key environmental factor affecting tipburn severity in commercial crops. However, there are limited studies comparing the occurrence of tipburn and calcium (Ca) distribution in lisianthus cultivars under different relative air humidity conditions. Accordingly, we investigated the effect of relative air humidity on tipburn severity, transpiration rate, and Ca content in seven lisianthus cultivars. Under a high humidity treatment (70%), only two cultivars (“Voyage pink” (VP) and “Azuma-no-kaori” (AK)) showed significantly higher tipburn severity than those under a low humidity treatment (50%), which suggests that high humidity conditions do not always increase tipburn severity in lisianthus. Transpiration rates of all cultivars, except for AK, were either significantly lower under the high humidity treatment than under the low humidity treatment, or did not vary significantly between the treatments. In contrast, total Ca concentrations in all cultivars, except for “Piccolosa snow” (PS), were significantly higher under the high humidity treatment than under the low humidity treatment. These results suggest that Ca acquisition and distribution in lisianthus cultivars are strongly influenced by Ca uptake from root pressure.

Description: Tipburn (calcium (Ca) deficiency disorder) is a major problem in the production of lisianthus cultivars. However, few studies have investigated the influence of different Ca concentrations in nutrient solution on tipburn incidence and Ca acquisition and distribution. Thus, it remains unclear why some cultivars exhibit tipburn under high Ca concentrations. To address this, we used three lisianthus cultivars ‘Azuma-no-Kaori’ (AK), ‘Celeb Wine’ (CW), and ‘Voyage Yellow’ (VY) and compared tipburn incidence and Ca acquisition and distribution under different Ca concentrations in a nutrient solution (low (40 ppm), moderate (80 ppm), and high (120 ppm) Ca). Tipburn severity and incidence in AK and VY significantly decreased with increasing nutritional Ca concentrations; the Ca concentrations in each organ and Ca acquisition competence (RGRCa) increased at higher nutritional Ca concentrations. In contrast, tipburn incidence in CW was 100% for all treatments. In CW, Ca acquisition competence and Ca concentrations in most organs increased with increasing nutritional Ca concentrations, but the Ca concentrations in the tips of the upper leaves did not differ significantly between treatments. Thus, our results suggest that the cause of tipburn under sufficient Ca conditions is an inability of the plant to distribute Ca to the tips of its upper leaves.

Description: Occurrence of tipburn is a severe problem in the production of lisianthus cultivars. Previous studies have shown excessive Ca accumulation in the roots of tipburn-damaged cultivars, where the distribution of Ca to the tips of the top leaves is inhibited. However, few studies have investigated the association between Ca accumulation and gene expression in horticultural crops. To provide a list of candidate target genes that might be causing the excessive Ca accumulation in roots, we focused Ca2+ transporter and pectin methylesterase (PME) genes and RNA-seq of upper leaves and roots in tipburn-occurrence cultivar (“Voyage peach”: VP) and non-occurrence cultivar (“Umi honoka”: UH) was conducted. In both the upper leaves and roots of VP, genes encoding the glutamate receptors (GLRs), cation/Ca2+ exchangers 4 (CCX4), Na+/Ca2+ exchanger-like protein (NCL), and PMEs were upregulated, and a gene encoding the cyclic nucleotide-gated ion channel 9 (CNGC9) was downregulated. In contrast, genes encoding the vacuolar cation/proton exchanger 5 (CAX5), calcium-transporting ATPase 1 and 12 (ACA1 and ACA12) showed differential expression in each organ. Among them, only CAX5 was upregulated and ACA12 was downregulated in the roots of VP. Based on these results, we suggested that CAX5 and ACA12 are the candidate genes causing the excessive Ca accumulation in the roots of tipburn-occurrence lisianthus cultivars. Future studies should investigate the temporal changes in gene expression using quantitative PCR and conduct functional analysis of candidate genes in tipburn-damaged lisianthus cultivars.

Description: The occurrence of calcium (Ca2+) deficiency disorders is a severe problem in the production of horticulture crops. Recently, several studies have investigated the role of gene expression in Ca2+ deficiency disorders and/or Ca2+ accumulation, providing an indication of the mechanism of Ca2+ deficiency disorders at the genetic level. To determine the relation between gene expression and the occurrence of Ca2+ deficiency disorders, we conducted a systematic review of the literature using the Preferred Reporting Items for Systematic Reviews and Meta-analyses protocol. In our initial search, we extracted studies investigating the relationships between Ca2+ deficiency disorders (tipburn and blossom-end rot) and gene expression. In our second search, we extracted studies involving functional analyses of the genes associated with Ca2+ deficiency and/or Ca2+ accumulation in plant organs. Thirty-seven articles were extracted from both searches. Studies on Ca2+ movement-related genes (Ca2+ antiporters, calreticulin, Ca2+ pumps, Ca2+ channels, and pectin methylesterases) accounted for the majority of these articles. Particularly, the effects of the expression of CAXs (Ca2+/H+ antiporters) and CRT (calreticulin) on the occurrence of Ca2+ deficiency disorders were demonstrated in studies extracted from both searches. Further research focusing on these genes may reveal the causative genes for Ca deficiency disorders in different horticulture crops. We hope that the knowledge synthesized in this systematic review will contribute to the accumulation of further knowledge and elucidation of the causes of Ca2+ deficiency disorders.