Rooted In Vitality

Fixed as they are, deep in the soil, plants can’t run from a threat. Instead, they’re left to their own devices to protect themselves from pathogens, parasites, herbivores, and the environment—and they do a pretty good job at it most of the time. While it’s a relatively new field of study, research shows that the strategies plants use to protect their vitality may have the same impact on ours.

Plant immunity basics

Unlike us, plants don’t have circulating antibodies or specialized immune cells to shield them from threats. To respond to their surroundings, plants developed a variety of defence strategies to cope with a vast array of unfavourable conditions.

For example, plants have barrier defences to protect themselves from herbivores, including protective bark, thorns, and tough cell walls. These shields are much like our own barrier defences, including skin and mucous membranes.

Plants have also developed sophisticated surveillance systems that recognize potentially dangerous pathogens and provide a rapid response when serious damage occurs. Basal resistance (also called innate immunity) refers to the first-line defences that protect plants against entire groups of pathogens, much like our own innate immunity.

Basal resistance is triggered when plant cells recognize microbe-associated molecular patterns (MAMPs) including proteins, lipopolysaccharides, and common microbial cell wall components. The result is that living plant cells become fortified against attack.

As can happen in humans, however, sometimes the pathogens have countermeasures that suppress first-line defences. If this occurs, plants employ the hypersensitive response, in which infected cells are sacrificed in a bid to save the entire plant.

This response is more pathogen-specific than basal resistance and is often triggered by bacteria, fungi, viruses, and nematodes (small worms). Once this response has been triggered, plant tissues may be set to high alert and become abundantly resistant to a broad range of pathogens for an extended period.

In another process, called RNA silencing, plants can identify foreign molecules of a virus and respond by digesting the genetic strands of the invader into useless fragments. Like our own adaptive immunity that remembers prior invaders, plants may be able to preserve a template of the digested genetic strand, which can facilitate a quick response if similar viruses attempt an attack in the future.

Phytochemical Defences

Plant chemicals can be divided into two major categories.

Primary metabolites are produced by all plant cells that are involved in growth, development, or reproduction and include the sugars, proteins, and amino acids we often think about as health benefits of eating plants.

Secondary or specialized metabolites are typically involved with matters of defence. These compounds usually belong to one of three large chemical classes:

• terpenes (plant volatiles, cardiac glycosides, carotenoids, and sterols)
• phenolics (phenolic acids, coumarins, lignans, stilbenes, flavonoids, tannins, and lignins)
• alkaloids (also glucosinolates)

Preliminary studies show that these plant-defending phytochemicals may play a role in delaying aging and related degenerative diseases in humans.

To Your Healthy Aging

Both aging and chronic diseases are associated with increased free radicals and subsequent oxidative damage, chronic low-grade inflammation, as well as accumulated DNA mutations. Obviously, then, reducing free-radical generation and easing inflammation are critical for healthy longevity.

Dietary metabolites may support our health by moderating cell signalling pathways and by acting as antioxidants—or boosting the effect of other antioxidants. Phenolic compounds suppress inflammatory processes, both in a similar way to nonsteroidal anti-inflammatory drugs such as aspirin and by inhibiting the activity of other pro-inflammatory pathways.

Phytochemicals appear to be protective against cancer, neurodegenerative disorders, and cardiovascular diseases, along with other chronic diseases of aging. Antiaging phytochemicals resveratrol, EGCG (in green tea), quercetin, and curcumin have been found to activate adenosine monophosphate (AMP)-activated protein kinase (AMPK), which is a fuel-sensing enzyme crucial for cellular homeostasis in response to metabolic stress. AMPK is a major focus for the treatment of metabolic diseases including type 2 diabetes and obesity.

There is also early evidence that phytonutrients may play a role in rejuvenating the immune system. For example, evidence suggests that the flavonoid quercetin (in apples, onions, and citrus fruit) can regenerate senescent (aging) fibroblasts, which are the cells that help form the structural framework of tissues and play an important role in tissue repair. Quercetin has been found to be the most potent free-radical scavenging flavonoid and also has a strong anti-inflammatory capacity.

Many phytonutrients, such as allicin in aged garlic, resveratrol in grape skins, and curcumin have been found, in laboratory studies, to promote longevity. Stay tuned for more research on the life-extending benefits of phytochemicals for humans!