If your snack has a core, it’s probably a pome. From its name you probably guessed that this bunch includes apples, as well as pears. If you’re a bit more adventurous, your favourite breakfast might include a multiple fruit, which is a fruit that is actually make up of a cluster of fruiting bodies. Some examples of this are pineapple, figs and mulberries. These fruits turn out to be part of a greater group called accessory fruits, in which the fruit (or many fruiting bodies) is not derived from the ovary, but some other part of the developing plant. This is where the “not-a-berry” strawberry falls.
Well, a berry has seeds and pulp (properly called “pericarp”) that develop from the ovary of a flower. The pericarp of all fruit is actually subdivided into 3 layers. The exocarp is the skin of the fruit, and in berries it’s often eaten (like in grapes) but not always (like in bananas). The mesocarp is the part of the fruit we usually eat, like the white yummy part of an apple, or the bulk of a plum, though in citrus fruits the mesocarp is actually the white, sort of inner-peel that we remove. Last is the endocarp, which is the closest layer that envelopes the seeds. In stone fruits, it’s the stone. In many fruits, it’s actually a membrane that we don’t really notice, often because it’s been bred to be thin, like in bananas. In citrus, the endocarp is actually the membrane that holds the juicy parts of the fruit, that is, the part you don’t want to pierce unless you want to get sticky.
So if your favourite fruit isn’t a berry, what might it be? If it has a thick, hard endocarp, it’s probably a drupe, a fancy term for a stone fruit. This group encompasses apricots, mangoes, cherries, olives, avocados, dates and most nuts. Basically, if you wouldn’t want to just bite into it, it’s probably a drupe.
If most fruit have these 3 layers, then why are berries special? It’s mostly due to the nature of their endocarps. Although not exactly quantified, berries generally have thin endocarps and fleshy (not dry) pericarps. Of course, these rules aren’t rigid, as watermelons and citrus fruits are berries, and neither are thought to have especially thin skins.
It turns out berry is actually a botanical term, not a common English one. It turns out that blackberries, mulberries, and raspberries are not berries at all, but bananas, pumpkins, avocados and cucumbers are. So what makes a berry?
Finally, if you, like me, consider your favourite fruit to be a raspberry or blackberry, then you love aggregate fruits. These are formed by many ovaries merging to become one flower, and most are also accessory fruits. Botany is weird, isn’t it?
14, 7, or 4 days delayed, respectively, in their ripening program at mid-véraison stage (Additional file 1) . Examination of the number and weight of seeds per berry revealed that green underripe berries consistently contained higher seed number and weight compared to the colored berries that had entered the ripening phase earlier even though the seeds had yet to reach their maximum weight (Figure 1A). This suggests that the delay in the ripening onset for individual berries increases along with the increasing seed content. A number of studies have indicated that seed number and weight are related to berry growth and showed a positive correlation between growth rates of seed and pericarp tissues during the first phase of berry development [4,7,22,31]. The entry of the pericarp into the ripening phase also generally coincides with the completion of seed growth . Two studies investigated the relationship between seed content, fruit growth and ripening in grape [22,32]. In these studies lower seed weight in Shiraz and low seed number in Concord were associated with delayed berry ripeness and the ripening delay was attributed to incomplete seed maturation . However, our results in Pinot noir show that green underripe berries have not only higher total seed weight per berry, but also the weights of individual seeds are significantly higher compared to those of red berries, suggesting a quantitative negative influence of seed tissue on the ripening (Additional file 2). These contrasting findings might be attributable to cultivar differences, to the method of defining berry seed content for which berry size differences were not considered, and to the exclusive use of seed weight or number in the interpretation of the results in the two studies cited in [22,32].
Observation of seed content and berry ripening phenotype
Screening for Auxin response genes induced in grape cultured cells and in the pericarp of low and high seed containing berries. (A) Induction of auxin response genes in cultured grape cells with auxin treatment (20 μM indole-3-acetic acid). The expression level is relative to the control. (B) Expression of auxin response genes in the pericarp of berries with low and high seed weight-to-berry weight (SB) from one-week prevéraison clusters. Expression level of high-SB is shown relative to that of low-SB. (C) Expression of ARF4 gene in the pericarp of low and high-SB berry groups at two- and one-week prevéraison (PV), and at mid-véraison (MV). Expression levels of ARF4 are relative to those of low-SB berries at 2-wk PV. Gene expression was analyzed by qRT-PCR and all data represent means of five replicates and error bars indicate ± SEM. Significant differences between low- and high-SB berries at each cluster stage are indicated by asterisks (Student’s t-test, p < 0.05). Significant differences of each SB group between the ripening stages are denoted by different letters (lower and upper case letters are used for low- and high-SB berries, respectively (Tukey’s HSD, p < 0.05)).
To examine the composition of green, pink, and red berries in the mid-véraison cluster originating from berries with low and high seed content, we segregated the berries on the basis of their “seed weight-to-berry weight ratio (SB)”, and refer to these as the low and high-SB groups hereafter. To rule out the effect of seed number on ripening, only the single-seeded berries, which accounted for
Botanically speaking, a berry has three distinct fleshy layers: the exocarp (outer skin), mesocarp (fleshy middle) and endocarp (innermost part, which holds the seeds). For instance, a grape’s outer skin is the exocarp, its fleshy middle is the mesocarp and the jelly-like insides holding the seeds constitute the endocarp, Jernstedt told Live Science.
“Raspberries have those little subunits,” Jernstedt said. “Each one of those little subunits comes from an individual ovary. And those subunits are actually [called] drupes.”
The same layered structure appears in other berries, including the banana and watermelon, although their exocarps are a bit tougher, taking the form of a peel and a rind, respectively. (The suffix “carp” comes from the word “carpel,” which refers to the pistil, the female organ of the flower, Jernstedt said.)