The cover image this week shows sunrise over purslane (Portulaca oleracea), specifically flowers of the Tequila Sunrise™ variety, so named because its colours match those of a popular cocktail of the same name. The image is to mark the earliest sunrise of the year which occurs this coming Wednesday (14th June).
You may have thought that earliest sunrise and latest sunset coincide on 21st June, the longest day of the year. Actually they occur a week earlier and a week later, respectively, a consequence of Earth’s eccentric orbit around the sun.
Portulaca featured in two previous leaves, about photosynthetic adaptations known as Crassulacean Acid Metabolism or CAM (Leaf 56 Crassulacean Colour and CO₂ https://lnkd.in/dbSbD6BG ).and C₄ photosynthesis. (Leaf 76 Portula C₄ a for your skin https://lnkd.in/dyctHAGU ), Portulaca is remarkable for showing both adaptations in the same plants. When it comes to sunrise/sunset, CAM is the more relevant. At night, Portulaca combines CO₂ and phosphoenylpyruvate (PEP) to make malic acid. In the day the CO₂ is released and refixed into sugars by conventional photosynthesis. Thus malate levels vary greatly during the day, almost fourfold in some Portulaca varieties (Ku,SB et al 1981).
Purslane is popular as a salad vegetable with a lemony taste due in part to malic acid. Plants harvested early morning taste significantly tangier. Purslane is also a traditional herbalmedicine, known in China as Ma Chi Xian (马齿苋), used to treat digestive tract disorders and bites and stings and sores on the skin. It is known to have bacterial, antifungal and antioxidative activities. The significant components include caffeic acid and flavonoids. Purslane for medicinal purposes is harvested without roots and dried but I have yet to find any directives about optimal time of day for harvesting, important because the content of important phytoactives surely changes during the day. I suggest that deciding when in the day to harvest might be important for many medicinal plants, just as it is for winemakers harvesting their grapes.
Further reading
• Ferrari RC (2020). Exploring C4-CAM plasticity within the Portulaca oleracea complex. Scientific reports, 10(1),14237. https://doi.org/10.1038/s41598-020-71012-y
•Article about Purslane, White RabbitInstitute, https://www.whiterabbitinstituteofhealing.com/herbs/purslane/
• Ku, SB et al (1981). Photosynthetic Characteristics of Portulaca grandiflora, a Succulent C₄ Dicot: CELLULAR COMPARTMENTATION OF ENZYMES ANDACID METABOLISM. Plant physiology, 68(5), 1073–1080. https://doi.org/10.1104/pp.68.5.1073
