Reduced Photoinhibition under Low Irradiance Enhanced Kacip Fatimah (Labisia pumila Benth) Secondary Metabolites, Phenyl Alanine Lyase and Antioxidant Activity

A randomized complete block design experiment was designed to characterize the relationship between production of total flavonoids and phenolics, anthocyanin, photosynthesis, maximum efficiency of photosystem II (Fv/Fm), electron transfer rate (Fm/Fo), phenyl alanine lyase activity (PAL) and antioxidant (DPPH) in Labisia pumila var. alata, under four levels of irradiance (225, 500, 625 and 900 μmol/m2/s) for 16 weeks. As irradiance levels increased from 225 to 900 μmol/m2/s, the production of plant secondary metabolites (total flavonoids, phenolics and antocyanin) was found to decrease steadily. Production of total flavonoids and phenolics reached their peaks under 225 followed by 500, 625 and 900 μmol/m2/s irradiances. Significant positive correlation of production of total phenolics, flavonoids and antocyanin content with Fv/Fm, Fm/Fo and photosynthesis indicated up-regulation of carbon-based secondary metabolites (CBSM) under reduced photoinhibition on the under low light levels condition. At the lowest irradiance levels, Labisia pumila extracts also exhibited a significantly higher antioxidant activity (DPPH) than under high irradiance. The improved antioxidative activity under low light levels might be due to high availability of total flavonoids, phenolics and anthocyanin content in the plant extract. It was also found that an increase in the production of CBSM was due to high PAL activity under low light, probably signifying more availability of phenylalanine (Phe) under this condition

THE BARBALOIN CONTENT AND DISTRIBUTION IN ALOE ARBORESCENS LEAVES ACCORDING TO THE LEAF PART, AGE, POSITION, AND SEASON

The distribution of the secondary phenolic compound, barbaloin, in Aloe arborescens leaves depends on the leaf part, age, and position of the leaf, as well as on seasonal influences. Young and old leaves of A. arborescens were cut from plants monthly and the exudate was immediately freeze-dried. The barbaloin levels were determined spectrophotometrically at λmax, 360–362 nm after separation by TLC. In all leaves the tissue of the basal third of the leaf had the lowest barbaloin content, the upper third contained the highest percentage, and the middle part contained the intermediate percentage. After cutting young leaves, the new basal part that grows after replanting has a higher barbaloin content after about five months when compared with the same part before cutting. In the 16 leaves of a cutting rooted two years before the experiment, the highest barbaloin content was found in the four upper young leaves (63%). In all the other leaves the barbaloin content was found to be only between 13 and 22%. There are also seasonal influences on the barbaloin content of young leaves. When old and young leaves were compared, the higher barbaloin content was found in the young leaves harvested at the same time.</jats:p

Influences of leaf pruning on the content of the secondary phenolic metabolites barbaloin, aloeresin and aloenin, in the leaves of Aloe arborescens

The content of three secondary phenolic metabolites (SPMs) barbaloin, aloeresin and aloenin, in Aloe arborescens is the highest in leaf two. The lower the leaf on the branch, the lower is the content of SPMs. The content of SPMs also differs in the various parts of each leaf. The highest amounts are found along the margins of the upper third of the leaf and the lowest at the centre of the leaf base. After pruning a leaf, the SPMs content in the regrown part of that leaf is higher than in another plant with unpruned leaves. Repeated leaf pruning can gradually increase the SPMs content of the dry exudate of regrown parts from 12-86%. The higher the pruned leaf is on the branch, the greater the increase in the content of SPMs in the regrown parts of the leaf. Such leaf pruning also increases the content of SPMs in the leaf located opposite the pruned leaf, but a greater increase occurs in the new young leaf at the top of the branch. Pruning leaf two gradually increases the content of SPMs in the lower leaves. The higher the leaf, the greater the increase

Leaf age, position and anatomical influences on the distribution of the secondary metabolites, homonataloin and three isomers of aloeresin in Aloe hereroensis (Aloaceae) leaves

Twenty leaves belonging to five age groups from four different Aloe hereroensis plants were investigated by anatomical and TLC methods. These results indicated that most of the phenolic metabolites are located in the vascular bundle sheath. The homonataloin accumulates in the big inner bundle sheath parenchymatous cells and the three isomers of aloeresin isomers are mainly located in the outer bundle sheath cells. Therefore, the different content of these secondary metabolites in the various leaf parts, and different leaf ages, of Aloe hereroensis are positively related to the density of the vascular bundles. Of all 20 leaves, the top thirds had similar density of vascular bundles, as well as the highest content of the secondary metabolites. However, between the top, middle and the base leaf thirds, both the density of vascular bundles and the content of secondary metabolites were significantly different. In the same leaf, the top third has the highest density of vascular bundles, the base the lowest and the middle an intermediate density. The more exposed the younger leaves and the leaf parts to consumption, the higher the content of the secondary metabolites. This distribution of phenolic metabolites in leaves seems to relate to defense strategies of a plant